Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

30 files changed, 9022 insertions, 0 deletions

diff --git a/third_party/python/pyrsistent/CHANGES.txt b/third_party/python/pyrsistent/CHANGES.txt
new file mode 100644
index 0000000000..603b3f2048
--- /dev/null
+++ b/third_party/python/pyrsistent/CHANGES.txt
@@ -0,0 +1,333 @@
+Revision history
+----------------
+0.16.0, 2020-03-24
+ * No major updates but Python 2 support no longer guaranteed.
+ * Fix #192, 'ignore_extra' for 'pvector_field'. Thanks @ss18 for this!
+ * Fix #191, include LICENCE in distribution. Thanks @johnthagen for this!
+ * Fix #190, minor MyPy errors. Thanks @Qhesz for this!
+
+0.15.7, 2020-01-07
+ * NOTE! This is the last version of Pyrsistent that officially supports Python 2.X!
+ * Fix #186, type errors with more recent versions of MyPy. Thanks @qhesz for this!
+ * Build and test on ARM during CI. Thanks @ossdev07 for this!
+ * Set absolute imports for python2 compatibility. Thanks @michalvi for this!
+
+0.15.6, 2019-11-23
+ * Fix #182 moduleinit name clash.
+
+0.15.5, 2019-10-27
+ * Fix #179 Fixed 'ignore_extra' factory parameter for pvector. Thanks @ss18 for this!
+
+0.15.4, 2019-07-27
+ * Fix #174, fix a GC traversal bug in pvector evolver C extension. Thanks @till-varoquaux for finding and fixing this!
+ * Fix #175, pytest 5 compatibility, this is a quick fix, some more work is needed to get coverage working etc.
+
+0.15.3, 2019-07-07
+ * Fix #172, catch all exceptions during extension build to reduce chance of corner cases that prevents installation.
+ * Fix #171, in PVector equality comparison don's assume that other object has a length, check before calling len.
+ * Fix #168, write warning about failing build of C extension directly to stderr to avoid that pip silences it.
+ * Fix #155, update PMapEvolver type stub to better reflect implementation.
+
+0.15.2, 2019-05-12
+ * Fix #166, Propagate 'ignore_extra' param in hierarchy. Thanks @ss18 for this!
+ * Fix #167, thaw typing. Thanks @nattofriends for this!
+ * Fix #154, not possible to insert empty pmap as leaf node with transform.
+
+0.15.1, 2019-04-26
+ * Fix #163 installation broken on Python 2 because of fix of #161, thanks @vphilippon for this! Sorry for the
+   inconvenience.
+
+0.15.0, 2019-04-25
+ * Python 3.4 is no longer officially supported since it is EOL since 2019-03-18.
+ * Fix #157, major improvements to type hints. Thanks @je-l for working on this and @nattofriend for reviewing the PR!
+ * Fix #161, installation fails on some Windows platforms because fallback to Python pvector does not work.
+   Thanks @MaxTaggart for fixing and verifying this!
+
+0.14.11, 2019-02-21
+ * Fix #152 Don't use __builtin_popcount, this hopefully fixes #147 Error in pvectorc.cp37-win_amd64.pyd file, as well.
+   Thanks @benrg for this!
+ * Fix #151 Fix compatibility for hypothesis 4. Thanks @felixonmars for this!
+
+0.14.10, 2019-02-09
+ * Fix #148, only require pytest-runner if running tests. Thanks @ccorbacho for this!
+
+0.14.9, 2019-01-06
+ * Fix #144, Compile pvectormodule.c on windows. Thanks @ganwell for this!
+
+0.14.8, 2018-12-19
+ * Fix #142, Improve type stubs. Thanks @arxanas for this!
+
+0.14.7, 2018-11-20
+ * Fix #102, add PEP 561 type annotation stubs for most pyrsistent types. Thanks @nattofriends for this!
+
+0.14.6, 2018-11-17
+ * Fix #135, Type classes for Python 3 type annotations of pyrsistent types. Thanks @nattofriends for this!
+ * Fix #128, Allow PClass and PRecord to ignore input parameters to constructor that are not part of the spec
+   instead of blowing up with a type error. Thanks @agberk for this!
+
+0.14.5, 2018-10-14
+ * Fix #137, deprecation warnings in Python 3.7. Thanks @thombashi for this!
+ * Fix #129, building via setuptools and setup.py. Thanks @galuszkak for this!
+
+0.14.4, 2018-07-08
+ * Fix #133, minor Python 3.7 compatibility issue. Pyrsistent is now officially Python 3.7 compliant!
+
+v0.14.3, 2018-06-11
+ * Fix #123 regression where type names break sequence fields. Thanks @doozr for this!
+ * Fix #124 using the class name to make AttributeError on __getattr__ more informative for PRecords.
+   Thanks @neilvyas for this!
+ * Fix #125 how fields handle type arguments. Thanks @neilvyas for this!
+
+v0.14.2, 2017-12-06
+ * Fix #121, regression in PClass.set() introduced in 0.14.1.
+
+v0.14.1, 2017-11-27
+ * Equality check performance improvements for pvectors and pmaps. Thanks @dtomas for this!
+ * Avoid calling factories multiple times for fields that do not change, see PR #120 for for
+   details. Thanks @teepark for this!
+
+v0.14.0, 2017-10-08
+ * Fix #117, pmap now accepts iterators as input to constructor. Thanks @Julian for this!
+ * Drop support for Python 2.6. Nothing has been done in this release that will explicitly
+   break pyrsistent for 2.6 but it will not be considered moving forward.  Dropping 2.6
+   support is the reason for stepping the second decimal instead of the third.
+
+v0.13.0, 2017-09-01
+ * Fix #113, Skip field factories when loading pickled objects. There is a
+   minor backwards incompatibilty in the behaviour because of this. Thanks
+   @teepark for fi this!
+ * Fix #116, negative indexing for pdeques. Thanks @Julian for this!
+
+v0.12.3, 2017-06-04
+ * Fix #83, make it possible to use Python 3 enums as field type without having to wrap it in
+   a list or tuple. Thanks @douglas-treadwell for this!
+
+v0.12.2, 2017-05-30
+ * Fix #108, now possible to use the values in predicates to transform. Thanks @exarkus for this!
+ * Fix #107, support multiple level of __invariant__ inheritance. Thanks @exarkus for this!
+
+v0.12.1, 2017-02-26
+ * Fix #97, initialize CheckedPVector from iterator-
+ * Fix #97, cache hash value on PMap. Thanks @sarum90 for this!
+
+v0.12.0, 2017-01-06
+ * Fix #87, add function get_in() for access to elements in deeply nested structures.
+ * Fix #91, add method update() to pset and pbag.
+ * Fix #92, incorrect discard of elements in transform on pvector
+ * This is a release candidate for 1.0 as I now consider pyrsistent fairly stable.
+
+v0.11.13, 2016-04-03
+ * Fix #84, pvector segfault in CPython 3 when repr of contained object raises Exception.
+ * Update README to cover for issue described in #83.
+
+v0.11.12, 2016-02-06
+ * Minor modifications of tests to allow testing as requested in #79 and #80.
+ * Also run CI tests under python 3.5
+
+v0.11.11, 2016-01-31
+ * #78, include tests in pypi dist.
+
+v0.11.10, 2015-12-27, NOTE! This release contains a backwards incompatible change
+                      despite only stepping the patch version number. See below.
+ * Implement #74, attribute access on PClass evolver
+ * Implement #75, lazily evaluated invariant messages by providing a
+   callable with no arguments.
+ * Initial values on fields can now be evaluated on object creation
+   by providing a callable with no arguments.
+
+   NOTE! If you previously had callables as initial values this change means that those
+         will be called upon object creation which may not be what you want. As
+         a temporary workaround a callable returning a callable can be used. This
+         feature and the concept of initial values will likely change slightly in the future.
+         See #77 and and #76 for more information.
+
+v0.11.9, 2015-11-01
+ * Added PVector.remove(), thanks @radix for initiating this!
+
+v0.11.8, 2015-10-18
+ * Fix #66, UnicodeDecodeError when doing pip install in environments with ascii encoding as default.
+   Thanks @foolswood!
+ * Implement support for multiple types in pmap_field(), pvector_field() and pset_field(). Thanks @itamarst!
+
+v0.11.7, 2015-10-03
+ * Fix #52, occasional SEGFAULTs due to misplaced call to PyObject_GC_Track. Thanks @jkbjh for this!
+ * Fix #42, complete support for delete. Now also on the C-implementation of the PVectorEvolver.
+   Thanks @itamarst for contributing a whole bunch of Hypothesis test cases covering the evolver operations!
+
+v0.11.6, 2015-09-30
+ * Add +, -, & and | operations to PBag. Thanks @Futrell for this!
+
+v0.11.5, 2015-09-29
+ * Fix bug introduced in 0.11.4 that prevented multi level inheritance from PClass.
+ * Make PClassMeta public for friendlier subclassing
+
+v0.11.4, 2015-09-28
+ * Fix #59, make it possible to create weakrefs to all collection types.
+   Thanks @itamarst for reporting it.
+ * Fix #58, add __str__ to InvariantException. Thanks @tomprince for reporting it.
+
+v0.11.3, 2015-09-15
+  * Fix #57, support pickling of PClasses and PRecords using pmap_field, pvector_field, and pset_field.
+    Thanks @radix for reporting this and submitting a fix for it!
+
+v0.11.2, 2015-09-09
+  * Fix bug causing potential element loss when reallocating PMap. Thanks to @jml for finding
+    this and submitting a PR with a fix!
+  * Removed python 3.2 test build from Travis. There is nothing breaking 3.2 compatibility in this
+    release but there will be no effort moving forward to keep the 3.2 compatibility.
+
+v0.11.1, 2015-08-24
+  * Fix #51, PClass.set() broken when used with string+value argument.
+  * #50, make it possible to specify more than one assertion in an invariant
+  * #48, make it possible to make recursive type references by using a string
+    as type specification.
+
+v0.11.0, 2015-07-11
+  * #42, delete() function added to PVector to allow deletion of elements by index
+    and range. Will perform a full copy of the vector, no structural sharing.
+    Thanks @radix for helping out with this one!
+  * Fix #39, explicitly disallow ordering for PMap and PBag, Python 3 style
+  * Fix #37, PMap.values()/keys()/items() now returns PVectors instead of lists
+
+v0.10.3, 2015-06-13
+  * Fix #40, make it possible to disable the C extension by setting the
+    PYRSISTENT_NO_C_EXTENSION environment variable.
+
+v0.10.2, 2015-06-07
+  * Fix #38, construction from serialized object for pvector/pset/pmap fields.
+
+v0.10.1, 2015-04-27
+  * Fix broken README.rst
+
+v10.0.0, 2015-04-27
+  * New type PClass, a persistent version of a Python object. Related to issues #30 and #32.
+    Thanks @exarkun and @radix for input on this one!
+  * Rename PRecordTypeError -> PTypeError, it is now also raised by PClass
+  * New convenience functions, pvector_field, pmap_field and pset_field to create PRecord/PClass
+    fields for checked collections. Issues #26 and #36. Thanks to @itamarst for this!
+  * Removed deprecated function set_in() on PMap and PVector.
+  * Removed deprecated factory function pclass.
+  * Major internal restructuring breaking pyrsistent.py into multiple files. This should
+    not affect those only using the public interface but if you experience problems please
+    let me know.
+
+v0.9.4, 2015-04-20
+  * Fix #34, PVector now compares against built in list type
+
+v0.9.3, 2015-04-06
+  * Rename pclass back to immutable and deprecate the usage of the pclass function. PClass will be used by
+    a new, different type in upcoming releases.
+  * Documentation strings for the exceptions introduced in 0.9.2.
+
+v0.9.2, 2015-04-03
+  * More informative type errors from checked types, issue #30
+  * Support multiple optional types, issue #28
+
+v0.9.1, 2015-02-25
+  * Multi level serialization for checked types
+
+v0.9.0, 2015-02-25, Lots of new stuff in this release!
+  * Checked types, checked versions of PVector, PMap, PSet that support type and invariant specification.
+    Currently lacking proper documentation but I'm working on it.
+  * set_in() on PVector and PMap are now deprecated and will be removed in the next release.
+    Use transform() instead. set_in() has been updated to use transform() for this release
+    this means that some corner error cases behave slightly different than before.
+  * Refactoring of the PVector to unify the type. Should not have any user impact as long as
+    only the public interface of pyrsistent has been used. PVector is now an abstract base class
+    with which the different implementations are registered.
+  * Evolvers have been updated to return themselves for evolving operations to allow function chaining.
+  * Richer exception messages for KeyErrors and IndexErrors specifying the key/index that caused the failure.
+    Thanks @radix for this.
+  * Missing attribute on PMaps when accessing with dot-notation now raises an AttributeError instead of a
+    KeyError. Issue #21.
+  * New function decorator @mutant that freezes all input arguments to a function and the return value.
+  * Add __version__ to pyrsistent.py. Issue #23.
+  * Fix pickling for pset. Issue #24.
+
+v0.8.0, 2015-01-21
+  * New type PRecord. Subtype of PMap that allows explicit, declarative field specification. Thanks @boxed
+    for inspiration!
+  * Efficient transformations of arbitrary complexity on PMap and PVector. Thanks @boxed for inspiration!
+  * Breaking change to the evolver interface. What used to be .pvector(), .pmap() and .pset()
+    on the different evolvers has now been unified so that all evolvers have one method .persistent()
+    to produce the persistent counterpart. Sorry for any inconvenience.
+  * Removed the tests directory from the package.
+  * PMap and PSet now contains a copy-function to closer mimic the interface of the dict and set. These
+    functions will simply return a reference to self.
+  * Removed deprecated alias 'immutable' from pclass.
+
+v0.7.1, 2015-01-17
+  * Fixes #14 where a file executed (unexpectedly) during installation was not python 3 compatible.
+
+v0.7.0, 2015-01-04, No 1.0, instead a bunch of new stuff and one API breaking change to PMap.remove().
+  * Evolvers for pvector, pmap and pset to allow simple and efficient updates of multiple elements
+    in the collection. See the documentation for a closer description.
+  * New method mset on pvector to update multiple values in one operation
+  * Remove deprecated methods merge and merge_with on PMap
+  * Change behavior of PMap.remove, it will now raise a KeyError if the element is not present.
+    New method PMap.discard will instead return the original pmap if the element is not present.
+    This aligns the PMap with how things are done in the PSet and is closer to the behavior of the
+    built in counterparts.
+
+v0.6.3, 2014-11-27
+  * Python 2.6 support, thanks @wrmsr!
+  * PMap.merge/merge_with renamed to update/update_with. merge/merge_with remains but will be
+    removed for 1.0.
+  * This is a release candidate for 1.0! Please be aware that PMap.merge/merge_with and immutable()
+    will be removed for 1.0.
+
+v0.6.2, 2014-11-03
+  * Fix typo causing the pure python vector to be used even if the C implementation was
+    available. Thanks @zerc for finding it!
+
+v0.6.1, 2014-10-31
+  * Renamed 'immutable' to 'pclass' for consistency but left immutable for compatibility.
+
+v0.6.0, 2014-10-25
+  * New data structure, persistent linked list
+  * New data structure, persistent double ended queue
+
+v0.5.0, 2014-09-24
+  * New data structure, persistent bag / multiset
+  * New functions freeze and thaw to recursively convert between python
+    built in data types and corresponding pyrsistent data types.
+  * All data structures can now be pickled
+  * New function merge_in on persistent map which allows a user
+    supplied function to implement the merge strategy.
+
+v0.4.0, 2014-09-20
+  * Full Python 3 support.
+  * Immutable object implemented.
+  * Bug fixes in PVector.__repr__() and PMap.__hash__() and index check of PVector.
+  * Repr changed to be fully cut and paste compatible
+  * Changed assoc() -> set(), assoc_in() -> set_in(), massoc() -> mset().
+    Sorry for the API breaking change but I think those names are more pythonic.
+  * Improved documentation.
+
+v0.3.1, 2014-06-29
+  * assoc() on PSet renamed back to add()
+
+v0.3.0, 2014-06-28
+  * Full Sequence protocol support for PVector
+  * Full Mapping protocol support for PMap
+  * Full Set protocol support for PSet
+  * assoc_in() support for both PMap and PVector
+  * merge() support for PMap
+  * Performance improvements to the PVector C extension speed up allocation
+
+v0.2.1, 2014-06-21
+  * Supply the tests with the distribution
+
+v0.2.0, 2014-06-21
+  * New C extension with an optimized version of the persistent vector
+  * Updated API slightly
+
+v0.1.0, 2013-11-10
+  * Initial release.
+
+
+TODO (in no particular order)
+-----------------------------
+- Versioned data structure where the different versions can be accessed by index?
+- Ordered sets and maps
+- A good performance measurement suite
diff --git a/third_party/python/pyrsistent/LICENCE.mit b/third_party/python/pyrsistent/LICENCE.mit
new file mode 100644
index 0000000000..6609e4c05a
--- /dev/null
+++ b/third_party/python/pyrsistent/LICENCE.mit
@@ -0,0 +1,22 @@
+Copyright (c) 2019 Tobias Gustafsson
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
\ No newline at end of file
diff --git a/third_party/python/pyrsistent/MANIFEST.in b/third_party/python/pyrsistent/MANIFEST.in
new file mode 100644
index 0000000000..155c6351bb
--- /dev/null
+++ b/third_party/python/pyrsistent/MANIFEST.in
@@ -0,0 +1,5 @@
+include *.rst
+include tests/*_test.py
+include tests/memory_profiling.py
+include CHANGES.txt
+include LICENCE.mit
\ No newline at end of file
diff --git a/third_party/python/pyrsistent/PKG-INFO b/third_party/python/pyrsistent/PKG-INFO
new file mode 100644
index 0000000000..1d1c159034
--- /dev/null
+++ b/third_party/python/pyrsistent/PKG-INFO
@@ -0,0 +1,742 @@
+Metadata-Version: 1.1
+Name: pyrsistent
+Version: 0.16.0
+Summary: Persistent/Functional/Immutable data structures
+Home-page: http://github.com/tobgu/pyrsistent/
+Author: Tobias Gustafsson
+Author-email: tobias.l.gustafsson@gmail.com
+License: MIT
+Description: Pyrsistent
+        ==========
+        .. image:: https://travis-ci.org/tobgu/pyrsistent.png?branch=master
+            :target: https://travis-ci.org/tobgu/pyrsistent
+        
+        .. image:: https://badge.fury.io/py/pyrsistent.svg
+            :target: https://badge.fury.io/py/pyrsistent
+        
+        .. image:: https://coveralls.io/repos/tobgu/pyrsistent/badge.svg?branch=master&service=github
+            :target: https://coveralls.io/github/tobgu/pyrsistent?branch=master
+        
+        
+        .. _Pyrthon: https://www.github.com/tobgu/pyrthon/
+        
+        Pyrsistent is a number of persistent collections (by some referred to as functional data structures). Persistent in 
+        the sense that they are immutable.
+        
+        All methods on a data structure that would normally mutate it instead return a new copy of the structure containing the
+        requested updates. The original structure is left untouched.
+        
+        This will simplify the reasoning about what a program does since no hidden side effects ever can take place to these
+        data structures. You can rest assured that the object you hold a reference to will remain the same throughout its
+        lifetime and need not worry that somewhere five stack levels below you in the darkest corner of your application
+        someone has decided to remove that element that you expected to be there.
+        
+        Pyrsistent is influenced by persistent data structures such as those found in the standard library of Clojure. The
+        data structures are designed to share common elements through path copying.
+        It aims at taking these concepts and make them as pythonic as possible so that they can be easily integrated into any python
+        program without hassle.
+        
+        If you want to go all in on persistent data structures and use literal syntax to define them in your code rather
+        than function calls check out Pyrthon_.
+        
+        Examples
+        --------
+        .. _Sequence: collections_
+        .. _Hashable: collections_
+        .. _Mapping: collections_
+        .. _Mappings: collections_
+        .. _Set: collections_
+        .. _collections: https://docs.python.org/3/library/collections.abc.html
+        .. _documentation: http://pyrsistent.readthedocs.org/
+        
+        The collection types and key features currently implemented are:
+        
+        * PVector_, similar to a python list
+        * PMap_, similar to dict
+        * PSet_, similar to set
+        * PRecord_, a PMap on steroids with fixed fields, optional type and invariant checking and much more
+        * PClass_, a Python class fixed fields, optional type and invariant checking and much more
+        * `Checked collections`_, PVector, PMap and PSet with optional type and invariance checks and more
+        * PBag, similar to collections.Counter
+        * PList, a classic singly linked list
+        * PDeque, similar to collections.deque
+        * Immutable object type (immutable) built on the named tuple
+        * freeze_ and thaw_ functions to convert between pythons standard collections and pyrsistent collections.
+        * Flexible transformations_ of arbitrarily complex structures built from PMaps and PVectors.
+        
+        Below are examples of common usage patterns for some of the structures and features. More information and
+        full documentation for all data structures is available in the documentation_.
+        
+        .. _PVector:
+        
+        PVector
+        ~~~~~~~
+        With full support for the Sequence_ protocol PVector is meant as a drop in replacement to the built in list from a readers
+        point of view. Write operations of course differ since no in place mutation is done but naming should be in line
+        with corresponding operations on the built in list.
+        
+        Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+        
+        Appends are amortized O(1). Random access and insert is log32(n) where n is the size of the vector.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import v, pvector
+        
+            # No mutation of vectors once created, instead they
+            # are "evolved" leaving the original untouched
+            >>> v1 = v(1, 2, 3)
+            >>> v2 = v1.append(4)
+            >>> v3 = v2.set(1, 5)
+            >>> v1
+            pvector([1, 2, 3])
+            >>> v2
+            pvector([1, 2, 3, 4])
+            >>> v3
+            pvector([1, 5, 3, 4])
+        
+            # Random access and slicing
+            >>> v3[1]
+            5
+            >>> v3[1:3]
+            pvector([5, 3])
+        
+            # Iteration
+            >>> list(x + 1 for x in v3)
+            [2, 6, 4, 5]
+            >>> pvector(2 * x for x in range(3))
+            pvector([0, 2, 4])
+        
+        .. _PMap:
+        
+        PMap
+        ~~~~
+        With full support for the Mapping_ protocol PMap is meant as a drop in replacement to the built in dict from a readers point
+        of view. Support for the Hashable_ protocol also means that it can be used as key in other Mappings_.
+        
+        Random access and insert is log32(n) where n is the size of the map.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import m, pmap, v
+        
+            # No mutation of maps once created, instead they are
+            # "evolved" leaving the original untouched
+            >>> m1 = m(a=1, b=2)
+            >>> m2 = m1.set('c', 3)
+            >>> m3 = m2.set('a', 5)
+            >>> m1
+            pmap({'a': 1, 'b': 2})
+            >>> m2
+            pmap({'a': 1, 'c': 3, 'b': 2})
+            >>> m3
+            pmap({'a': 5, 'c': 3, 'b': 2})
+            >>> m3['a']
+            5
+        
+            # Evolution of nested persistent structures
+            >>> m4 = m(a=5, b=6, c=v(1, 2))
+            >>> m4.transform(('c', 1), 17)
+            pmap({'a': 5, 'c': pvector([1, 17]), 'b': 6})
+            >>> m5 = m(a=1, b=2)
+        
+            # Evolve by merging with other mappings
+            >>> m5.update(m(a=2, c=3), {'a': 17, 'd': 35})
+            pmap({'a': 17, 'c': 3, 'b': 2, 'd': 35})
+            >>> pmap({'x': 1, 'y': 2}) + pmap({'y': 3, 'z': 4})
+            pmap({'y': 3, 'x': 1, 'z': 4})
+        
+            # Dict-like methods to convert to list and iterate
+            >>> m3.items()
+            pvector([('a', 5), ('c', 3), ('b', 2)])
+            >>> list(m3)
+            ['a', 'c', 'b']
+        
+        .. _PSet:
+        
+        PSet
+        ~~~~
+        With full support for the Set_ protocol PSet is meant as a drop in replacement to the built in set from a readers point
+        of view. Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+        
+        Random access and insert is log32(n) where n is the size of the set.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import s
+        
+            # No mutation of sets once created, you know the story...
+            >>> s1 = s(1, 2, 3, 2)
+            >>> s2 = s1.add(4)
+            >>> s3 = s1.remove(1)
+            >>> s1
+            pset([1, 2, 3])
+            >>> s2
+            pset([1, 2, 3, 4])
+            >>> s3
+            pset([2, 3])
+        
+            # Full support for set operations
+            >>> s1 | s(3, 4, 5)
+            pset([1, 2, 3, 4, 5])
+            >>> s1 & s(3, 4, 5)
+            pset([3])
+            >>> s1 < s2
+            True
+            >>> s1 < s(3, 4, 5)
+            False
+        
+        .. _PRecord:
+        
+        PRecord
+        ~~~~~~~
+        A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
+        from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
+        access using subscript notation.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import PRecord, field
+            >>> class ARecord(PRecord):
+            ...     x = field()
+            ...
+            >>> r = ARecord(x=3)
+            >>> r
+            ARecord(x=3)
+            >>> r.x
+            3
+            >>> r.set(x=2)
+            ARecord(x=2)
+            >>> r.set(y=2)
+            Traceback (most recent call last):
+            AttributeError: 'y' is not among the specified fields for ARecord
+        
+        Type information
+        ****************
+        It is possible to add type information to the record to enforce type checks. Multiple allowed types can be specified
+        by providing an iterable of types.
+        
+        .. code:: python
+        
+            >>> class BRecord(PRecord):
+            ...     x = field(type=int)
+            ...     y = field(type=(int, type(None)))
+            ...
+            >>> BRecord(x=3, y=None)
+            BRecord(y=None, x=3)
+            >>> BRecord(x=3.0)
+            Traceback (most recent call last):
+            PTypeError: Invalid type for field BRecord.x, was float
+        
+        
+        Custom types (classes) that are iterable should be wrapped in a tuple to prevent their
+        members being added to the set of valid types.  Although Enums in particular are now 
+        supported without wrapping, see #83 for more information.
+        
+        Mandatory fields
+        ****************
+        Fields are not mandatory by default but can be specified as such. If fields are missing an
+        *InvariantException* will be thrown which contains information about the missing fields.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import InvariantException
+            >>> class CRecord(PRecord):
+            ...     x = field(mandatory=True)
+            ...
+            >>> r = CRecord(x=3)
+            >>> try:
+            ...    r.discard('x')
+            ... except InvariantException as e:
+            ...    print(e.missing_fields)
+            ...
+            ('CRecord.x',)
+        
+        Invariants
+        **********
+        It is possible to add invariants that must hold when evolving the record. Invariants can be
+        specified on both field and record level. If invariants fail an *InvariantException* will be
+        thrown which contains information about the failing invariants. An invariant function should
+        return a tuple consisting of a boolean that tells if the invariant holds or not and an object
+        describing the invariant. This object can later be used to identify which invariant that failed.
+        
+        The global invariant function is only executed if all field invariants hold.
+        
+        Global invariants are inherited to subclasses.
+        
+        .. code:: python
+        
+            >>> class RestrictedVector(PRecord):
+            ...     __invariant__ = lambda r: (r.y >= r.x, 'x larger than y')
+            ...     x = field(invariant=lambda x: (x > 0, 'x negative'))
+            ...     y = field(invariant=lambda y: (y > 0, 'y negative'))
+            ...
+            >>> r = RestrictedVector(y=3, x=2)
+            >>> try:
+            ...    r.set(x=-1, y=-2)
+            ... except InvariantException as e:
+            ...    print(e.invariant_errors)
+            ...
+            ('y negative', 'x negative')
+            >>> try:
+            ...    r.set(x=2, y=1)
+            ... except InvariantException as e:
+            ...    print(e.invariant_errors)
+            ...
+            ('x larger than y',)
+        
+        Invariants may also contain multiple assertions. For those cases the invariant function should
+        return a tuple of invariant tuples as described above. This structure is reflected in the
+        invariant_errors attribute of the exception which will contain tuples with data from all failed
+        invariants. Eg:
+        
+        .. code:: python
+        
+            >>> class EvenX(PRecord):
+            ...     x = field(invariant=lambda x: ((x > 0, 'x negative'), (x % 2 == 0, 'x odd')))
+            ...
+            >>> try:
+            ...    EvenX(x=-1)
+            ... except InvariantException as e:
+            ...    print(e.invariant_errors)
+            ...
+            (('x negative', 'x odd'),)
+        
+        
+        Factories
+        *********
+        It's possible to specify factory functions for fields. The factory function receives whatever
+        is supplied as field value and the actual returned by the factory is assigned to the field
+        given that any type and invariant checks hold.
+        PRecords have a default factory specified as a static function on the class, create(). It takes
+        a *Mapping* as argument and returns an instance of the specific record.
+        If a record has fields of type PRecord the create() method of that record will
+        be called to create the "sub record" if no factory has explicitly been specified to override
+        this behaviour.
+        
+        .. code:: python
+        
+            >>> class DRecord(PRecord):
+            ...     x = field(factory=int)
+            ...
+            >>> class ERecord(PRecord):
+            ...     d = field(type=DRecord)
+            ...
+            >>> ERecord.create({'d': {'x': '1'}})
+            ERecord(d=DRecord(x=1))
+        
+        Collection fields
+        *****************
+        It is also possible to have fields with ``pyrsistent`` collections.
+        
+        .. code:: python
+        
+           >>> from pyrsistent import pset_field, pmap_field, pvector_field
+           >>> class MultiRecord(PRecord):
+           ...     set_of_ints = pset_field(int)
+           ...     map_int_to_str = pmap_field(int, str)
+           ...     vector_of_strs = pvector_field(str)
+           ...
+        	
+        Serialization
+        *************
+        PRecords support serialization back to dicts. Default serialization will take keys and values
+        "as is" and output them into a dict. It is possible to specify custom serialization functions
+        to take care of fields that require special treatment.
+        
+        .. code:: python
+        
+            >>> from datetime import date
+            >>> class Person(PRecord):
+            ...     name = field(type=unicode)
+            ...     birth_date = field(type=date,
+            ...                        serializer=lambda format, d: d.strftime(format['date']))
+            ...
+            >>> john = Person(name=u'John', birth_date=date(1985, 10, 21))
+            >>> john.serialize({'date': '%Y-%m-%d'})
+            {'birth_date': '1985-10-21', 'name': u'John'}
+        
+        
+        .. _instar: https://github.com/boxed/instar/
+        
+        .. _PClass:
+        
+        PClass
+        ~~~~~~
+        A PClass is a python class with a fixed set of specified fields. PClasses are declared as python classes inheriting
+        from PClass. It is defined the same way that PRecords are and behaves like a PRecord in all aspects except that it
+        is not a PMap and hence not a collection but rather a plain Python object.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import PClass, field
+            >>> class AClass(PClass):
+            ...     x = field()
+            ...
+            >>> a = AClass(x=3)
+            >>> a
+            AClass(x=3)
+            >>> a.x
+            3
+        
+        
+        Checked collections
+        ~~~~~~~~~~~~~~~~~~~
+        Checked collections currently come in three flavors: CheckedPVector, CheckedPMap and CheckedPSet.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import CheckedPVector, CheckedPMap, CheckedPSet, thaw
+            >>> class Positives(CheckedPSet):
+            ...     __type__ = (long, int)
+            ...     __invariant__ = lambda n: (n >= 0, 'Negative')
+            ...
+            >>> class Lottery(PRecord):
+            ...     name = field(type=str)
+            ...     numbers = field(type=Positives, invariant=lambda p: (len(p) > 0, 'No numbers'))
+            ...
+            >>> class Lotteries(CheckedPVector):
+            ...     __type__ = Lottery
+            ...
+            >>> class LotteriesByDate(CheckedPMap):
+            ...     __key_type__ = date
+            ...     __value_type__ = Lotteries
+            ...
+            >>> lotteries = LotteriesByDate.create({date(2015, 2, 15): [{'name': 'SuperLotto', 'numbers': {1, 2, 3}},
+            ...                                                         {'name': 'MegaLotto',  'numbers': {4, 5, 6}}],
+            ...                                     date(2015, 2, 16): [{'name': 'SuperLotto', 'numbers': {3, 2, 1}},
+            ...                                                         {'name': 'MegaLotto',  'numbers': {6, 5, 4}}]})
+            >>> lotteries
+            LotteriesByDate({datetime.date(2015, 2, 15): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')]), datetime.date(2015, 2, 16): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])})
+        
+            # The checked versions support all operations that the corresponding
+            # unchecked types do
+            >>> lottery_0215 = lotteries[date(2015, 2, 15)]
+            >>> lottery_0215.transform([0, 'name'], 'SuperDuperLotto')
+            Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperDuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])
+        
+            # But also makes asserts that types and invariants hold
+            >>> lottery_0215.transform([0, 'name'], 999)
+            Traceback (most recent call last):
+            PTypeError: Invalid type for field Lottery.name, was int
+        
+            >>> lottery_0215.transform([0, 'numbers'], set())
+            Traceback (most recent call last):
+            InvariantException: Field invariant failed
+        
+            # They can be converted back to python built ins with either thaw()
+            # or serialize() (which provides possibilities to customize serialization)
+            >>> thaw(lottery_0215)
+            [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+            >>> lottery_0215.serialize()
+            [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+        
+        .. _transformations:
+        
+        Transformations
+        ~~~~~~~~~~~~~~~
+        Transformations are inspired by the cool library instar_ for Clojure. They let you evolve PMaps and PVectors
+        with arbitrarily deep/complex nesting using simple syntax and flexible matching syntax.
+        
+        The first argument to transformation is the path that points out the value to transform. The
+        second is the transformation to perform. If the transformation is callable it will be applied
+        to the value(s) matching the path. The path may also contain callables. In that case they are
+        treated as matchers. If the matcher returns True for a specific key it is considered for transformation.
+        
+        .. code:: python
+        
+            # Basic examples
+            >>> from pyrsistent import inc, freeze, thaw, rex, ny, discard
+            >>> v1 = freeze([1, 2, 3, 4, 5])
+            >>> v1.transform([2], inc)
+            pvector([1, 2, 4, 4, 5])
+            >>> v1.transform([lambda ix: 0 < ix < 4], 8)
+            pvector([1, 8, 8, 8, 5])
+            >>> v1.transform([lambda ix, v: ix == 0 or v == 5], 0)
+            pvector([0, 2, 3, 4, 0])
+        
+            # The (a)ny matcher can be used to match anything
+            >>> v1.transform([ny], 8)
+            pvector([8, 8, 8, 8, 8])
+        
+            # Regular expressions can be used for matching
+            >>> scores = freeze({'John': 12, 'Joseph': 34, 'Sara': 23})
+            >>> scores.transform([rex('^Jo')], 0)
+            pmap({'Joseph': 0, 'Sara': 23, 'John': 0})
+        
+            # Transformations can be done on arbitrarily deep structures
+            >>> news_paper = freeze({'articles': [{'author': 'Sara', 'content': 'A short article'},
+            ...                                   {'author': 'Steve', 'content': 'A slightly longer article'}],
+            ...                      'weather': {'temperature': '11C', 'wind': '5m/s'}})
+            >>> short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:25] + '...' if len(c) > 25 else c)
+            >>> very_short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:15] + '...' if len(c) > 15 else c)
+            >>> very_short_news.articles[0].content
+            'A short article'
+            >>> very_short_news.articles[1].content
+            'A slightly long...'
+        
+            # When nothing has been transformed the original data structure is kept
+            >>> short_news is news_paper
+            True
+            >>> very_short_news is news_paper
+            False
+            >>> very_short_news.articles[0] is news_paper.articles[0]
+            True
+        
+            # There is a special transformation that can be used to discard elements. Also
+            # multiple transformations can be applied in one call
+            >>> thaw(news_paper.transform(['weather'], discard, ['articles', ny, 'content'], discard))
+            {'articles': [{'author': 'Sara'}, {'author': 'Steve'}]}
+        
+        Evolvers
+        ~~~~~~~~
+        PVector, PMap and PSet all have support for a concept dubbed *evolvers*. An evolver acts like a mutable
+        view of the underlying persistent data structure with "transaction like" semantics. No updates of the original
+        data structure is ever performed, it is still fully immutable.
+        
+        The evolvers have a very limited API by design to discourage excessive, and inappropriate, usage as that would
+        take us down the mutable road. In principle only basic mutation and element access functions are supported.
+        Check out the documentation_ of each data structure for specific examples.
+        
+        Examples of when you may want to use an evolver instead of working directly with the data structure include:
+        
+        * Multiple updates are done to the same data structure and the intermediate results are of no
+          interest. In this case using an evolver may be a more efficient and easier to work with.
+        * You need to pass a vector into a legacy function or a function that you have no control
+          over which performs in place mutations. In this case pass an evolver instance
+          instead and then create a new pvector from the evolver once the function returns.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import v
+        
+            # In place mutation as when working with the built in counterpart
+            >>> v1 = v(1, 2, 3)
+            >>> e = v1.evolver()
+            >>> e[1] = 22
+            >>> e = e.append(4)
+            >>> e = e.extend([5, 6])
+            >>> e[5] += 1
+            >>> len(e)
+            6
+        
+            # The evolver is considered *dirty* when it contains changes compared to the underlying vector
+            >>> e.is_dirty()
+            True
+        
+            # But the underlying pvector still remains untouched
+            >>> v1
+            pvector([1, 2, 3])
+        
+            # Once satisfied with the updates you can produce a new pvector containing the updates.
+            # The new pvector will share data with the original pvector in the same way that would have
+            # been done if only using operations on the pvector.
+            >>> v2 = e.persistent()
+            >>> v2
+            pvector([1, 22, 3, 4, 5, 7])
+        
+            # The evolver is now no longer considered *dirty* as it contains no differences compared to the
+            # pvector just produced.
+            >>> e.is_dirty()
+            False
+        
+            # You may continue to work with the same evolver without affecting the content of v2
+            >>> e[0] = 11
+        
+            # Or create a new evolver from v2. The two evolvers can be updated independently but will both
+            # share data with v2 where possible.
+            >>> e2 = v2.evolver()
+            >>> e2[0] = 1111
+            >>> e.persistent()
+            pvector([11, 22, 3, 4, 5, 7])
+            >>> e2.persistent()
+            pvector([1111, 22, 3, 4, 5, 7])
+        
+        .. _freeze:
+        .. _thaw:
+        
+        freeze and thaw
+        ~~~~~~~~~~~~~~~
+        These functions are great when your cozy immutable world has to interact with the evil mutable world outside.
+        
+        .. code:: python
+        
+            >>> from pyrsistent import freeze, thaw, v, m
+            >>> freeze([1, {'a': 3}])
+            pvector([1, pmap({'a': 3})])
+            >>> thaw(v(1, m(a=3)))
+            [1, {'a': 3}]
+        
+        Compatibility
+        -------------
+        
+        Pyrsistent is developed and tested on Python 2.7, 3.5, 3.6, 3.7 and PyPy (Python 2 and 3 compatible). It will most
+        likely work on all other versions >= 3.4 but no guarantees are given. :)
+        
+        Compatibility issues
+        ~~~~~~~~~~~~~~~~~~~~
+        
+        .. _27: https://github.com/tobgu/pyrsistent/issues/27
+        
+        There is currently one known compatibility issue when comparing built in sets and frozensets to PSets as discussed in 27_.
+        It affects python 2 versions < 2.7.8 and python 3 versions < 3.4.0 and is due to a bug described in
+        http://bugs.python.org/issue8743.
+        
+        Comparisons will fail or be incorrect when using the set/frozenset as left hand side of the comparison. As a workaround
+        you need to either upgrade Python to a more recent version, avoid comparing sets/frozensets with PSets or always make
+        sure to convert both sides of the comparison to the same type before performing the comparison.
+        
+        Performance
+        -----------
+        
+        Pyrsistent is developed with performance in mind. Still, while some operations are nearly on par with their built in, 
+        mutable, counterparts in terms of speed, other operations are slower. In the cases where attempts at
+        optimizations have been done, speed has generally been valued over space.
+        
+        Pyrsistent comes with two API compatible flavors of PVector (on which PMap and PSet are based), one pure Python 
+        implementation and one implemented as a C extension. The latter generally being 2 - 20 times faster than the former.
+        The C extension will be used automatically when possible.
+        
+        The pure python implementation is fully PyPy compatible. Running it under PyPy speeds operations up considerably if 
+        the structures are used heavily (if JITed), for some cases the performance is almost on par with the built in counterparts.
+        
+        Type hints
+        ----------
+        
+        PEP 561 style type hints for use with mypy and various editors are available for most types and functions in pyrsistent.
+        
+        Type classes for annotating your own code with pyrsistent types are also available under pyrsistent.typing.
+        
+        Installation
+        ------------
+        
+        pip install pyrsistent
+        
+        Documentation
+        -------------
+        
+        Available at http://pyrsistent.readthedocs.org/
+        
+        Brief presentation available at http://slides.com/tobiasgustafsson/immutability-and-python/
+        
+        Contributors
+        ------------
+        
+        Tobias Gustafsson https://github.com/tobgu
+        
+        Christopher Armstrong https://github.com/radix
+        
+        Anders Hovmöller https://github.com/boxed
+        
+        Itamar Turner-Trauring https://github.com/itamarst
+        
+        Jonathan Lange https://github.com/jml
+        
+        Richard Futrell https://github.com/Futrell
+        
+        Jakob Hollenstein https://github.com/jkbjh
+        
+        David Honour https://github.com/foolswood
+        
+        David R. MacIver https://github.com/DRMacIver
+        
+        Marcus Ewert https://github.com/sarum90
+        
+        Jean-Paul Calderone https://github.com/exarkun
+        
+        Douglas Treadwell https://github.com/douglas-treadwell
+        
+        Travis Parker https://github.com/teepark
+        
+        Julian Berman https://github.com/Julian
+        
+        Dennis Tomas https://github.com/dtomas
+        
+        Neil Vyas https://github.com/neilvyas
+        
+        doozr https://github.com/doozr
+        
+        Kamil Galuszka https://github.com/galuszkak
+        
+        Tsuyoshi Hombashi https://github.com/thombashi
+        
+        nattofriends https://github.com/nattofriends
+        
+        agberk https://github.com/agberk
+        
+        Waleed Khan https://github.com/arxanas
+        
+        Jean-Louis Fuchs https://github.com/ganwell
+        
+        Carlos Corbacho https://github.com/ccorbacho
+        
+        Felix Yan https://github.com/felixonmars
+        
+        benrg https://github.com/benrg
+        
+        Jere Lahelma https://github.com/je-l
+        
+        Max Taggart https://github.com/MaxTaggart
+        
+        Vincent Philippon https://github.com/vphilippon
+        
+        Semen Zhydenko https://github.com/ss18
+        
+        Till Varoquaux  https://github.com/till-varoquaux
+        
+        Michal Kowalik https://github.com/michalvi
+        
+        ossdev07 https://github.com/ossdev07
+        
+        Kerry Olesen https://github.com/qhesz
+        
+        johnthagen https://github.com/johnthagen
+        
+        Contributing
+        ------------
+        
+        Want to contribute? That's great! If you experience problems please log them on GitHub. If you want to contribute code,
+        please fork the repository and submit a pull request.
+        
+        Run tests
+        ~~~~~~~~~
+        .. _tox: https://tox.readthedocs.io/en/latest/
+        
+        Tests can be executed using tox_.
+        
+        Install tox: ``pip install tox``
+        
+        Run test for Python 2.7: ``tox -epy27``
+        
+        Release
+        ~~~~~~~
+        * Update CHANGES.txt
+        * Update README with any new contributors and potential info needed.
+        * Update _pyrsistent_version.py
+        * python setup.py sdist upload
+        * Commit and tag with new version: git add -u . && git commit -m 'Prepare version vX.Y.Z' && git tag -a vX.Y.Z -m 'vX.Y.Z'
+        * Push commit and tags: git push && git push --tags
+        
+        Project status
+        --------------
+        Pyrsistent can be considered stable and mature (who knows, there may even be a 1.0 some day :-)). The project is
+        maintained, bugs fixed, PRs reviewed and merged and new releases made. I currently do not have time for development
+        of new features or functionality which I don't have use for myself. I'm more than happy to take PRs for new
+        functionality though!
+        
+        There are a bunch of issues marked with ``enhancement`` and ``help wanted`` that contain requests for new functionality
+        that would be nice to include. The level of difficulty and extend of the issues varies, please reach out to me if you're
+        interested in working on any of them.
+        
+        If you feel that you have a grand master plan for where you would like Pyrsistent to go and have the time to put into
+        it please don't hesitate to discuss this with me and submit PRs for it. If all goes well I'd be more than happy to add
+        additional maintainers to the project!
+        
+Platform: UNKNOWN
+Classifier: Intended Audience :: Developers
+Classifier: License :: OSI Approved :: MIT License
+Classifier: Operating System :: OS Independent
+Classifier: Programming Language :: Python :: 3.5
+Classifier: Programming Language :: Python :: 3.6
+Classifier: Programming Language :: Python :: 3.7
+Classifier: Programming Language :: Python :: Implementation :: PyPy
diff --git a/third_party/python/pyrsistent/README b/third_party/python/pyrsistent/README
new file mode 100644
index 0000000000..a4c24e49bd
--- /dev/null
+++ b/third_party/python/pyrsistent/README
@@ -0,0 +1,725 @@
+Pyrsistent
+==========
+.. image:: https://travis-ci.org/tobgu/pyrsistent.png?branch=master
+    :target: https://travis-ci.org/tobgu/pyrsistent
+
+.. image:: https://badge.fury.io/py/pyrsistent.svg
+    :target: https://badge.fury.io/py/pyrsistent
+
+.. image:: https://coveralls.io/repos/tobgu/pyrsistent/badge.svg?branch=master&service=github
+    :target: https://coveralls.io/github/tobgu/pyrsistent?branch=master
+
+
+.. _Pyrthon: https://www.github.com/tobgu/pyrthon/
+
+Pyrsistent is a number of persistent collections (by some referred to as functional data structures). Persistent in 
+the sense that they are immutable.
+
+All methods on a data structure that would normally mutate it instead return a new copy of the structure containing the
+requested updates. The original structure is left untouched.
+
+This will simplify the reasoning about what a program does since no hidden side effects ever can take place to these
+data structures. You can rest assured that the object you hold a reference to will remain the same throughout its
+lifetime and need not worry that somewhere five stack levels below you in the darkest corner of your application
+someone has decided to remove that element that you expected to be there.
+
+Pyrsistent is influenced by persistent data structures such as those found in the standard library of Clojure. The
+data structures are designed to share common elements through path copying.
+It aims at taking these concepts and make them as pythonic as possible so that they can be easily integrated into any python
+program without hassle.
+
+If you want to go all in on persistent data structures and use literal syntax to define them in your code rather
+than function calls check out Pyrthon_.
+
+Examples
+--------
+.. _Sequence: collections_
+.. _Hashable: collections_
+.. _Mapping: collections_
+.. _Mappings: collections_
+.. _Set: collections_
+.. _collections: https://docs.python.org/3/library/collections.abc.html
+.. _documentation: http://pyrsistent.readthedocs.org/
+
+The collection types and key features currently implemented are:
+
+* PVector_, similar to a python list
+* PMap_, similar to dict
+* PSet_, similar to set
+* PRecord_, a PMap on steroids with fixed fields, optional type and invariant checking and much more
+* PClass_, a Python class fixed fields, optional type and invariant checking and much more
+* `Checked collections`_, PVector, PMap and PSet with optional type and invariance checks and more
+* PBag, similar to collections.Counter
+* PList, a classic singly linked list
+* PDeque, similar to collections.deque
+* Immutable object type (immutable) built on the named tuple
+* freeze_ and thaw_ functions to convert between pythons standard collections and pyrsistent collections.
+* Flexible transformations_ of arbitrarily complex structures built from PMaps and PVectors.
+
+Below are examples of common usage patterns for some of the structures and features. More information and
+full documentation for all data structures is available in the documentation_.
+
+.. _PVector:
+
+PVector
+~~~~~~~
+With full support for the Sequence_ protocol PVector is meant as a drop in replacement to the built in list from a readers
+point of view. Write operations of course differ since no in place mutation is done but naming should be in line
+with corresponding operations on the built in list.
+
+Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+
+Appends are amortized O(1). Random access and insert is log32(n) where n is the size of the vector.
+
+.. code:: python
+
+    >>> from pyrsistent import v, pvector
+
+    # No mutation of vectors once created, instead they
+    # are "evolved" leaving the original untouched
+    >>> v1 = v(1, 2, 3)
+    >>> v2 = v1.append(4)
+    >>> v3 = v2.set(1, 5)
+    >>> v1
+    pvector([1, 2, 3])
+    >>> v2
+    pvector([1, 2, 3, 4])
+    >>> v3
+    pvector([1, 5, 3, 4])
+
+    # Random access and slicing
+    >>> v3[1]
+    5
+    >>> v3[1:3]
+    pvector([5, 3])
+
+    # Iteration
+    >>> list(x + 1 for x in v3)
+    [2, 6, 4, 5]
+    >>> pvector(2 * x for x in range(3))
+    pvector([0, 2, 4])
+
+.. _PMap:
+
+PMap
+~~~~
+With full support for the Mapping_ protocol PMap is meant as a drop in replacement to the built in dict from a readers point
+of view. Support for the Hashable_ protocol also means that it can be used as key in other Mappings_.
+
+Random access and insert is log32(n) where n is the size of the map.
+
+.. code:: python
+
+    >>> from pyrsistent import m, pmap, v
+
+    # No mutation of maps once created, instead they are
+    # "evolved" leaving the original untouched
+    >>> m1 = m(a=1, b=2)
+    >>> m2 = m1.set('c', 3)
+    >>> m3 = m2.set('a', 5)
+    >>> m1
+    pmap({'a': 1, 'b': 2})
+    >>> m2
+    pmap({'a': 1, 'c': 3, 'b': 2})
+    >>> m3
+    pmap({'a': 5, 'c': 3, 'b': 2})
+    >>> m3['a']
+    5
+
+    # Evolution of nested persistent structures
+    >>> m4 = m(a=5, b=6, c=v(1, 2))
+    >>> m4.transform(('c', 1), 17)
+    pmap({'a': 5, 'c': pvector([1, 17]), 'b': 6})
+    >>> m5 = m(a=1, b=2)
+
+    # Evolve by merging with other mappings
+    >>> m5.update(m(a=2, c=3), {'a': 17, 'd': 35})
+    pmap({'a': 17, 'c': 3, 'b': 2, 'd': 35})
+    >>> pmap({'x': 1, 'y': 2}) + pmap({'y': 3, 'z': 4})
+    pmap({'y': 3, 'x': 1, 'z': 4})
+
+    # Dict-like methods to convert to list and iterate
+    >>> m3.items()
+    pvector([('a', 5), ('c', 3), ('b', 2)])
+    >>> list(m3)
+    ['a', 'c', 'b']
+
+.. _PSet:
+
+PSet
+~~~~
+With full support for the Set_ protocol PSet is meant as a drop in replacement to the built in set from a readers point
+of view. Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+
+Random access and insert is log32(n) where n is the size of the set.
+
+.. code:: python
+
+    >>> from pyrsistent import s
+
+    # No mutation of sets once created, you know the story...
+    >>> s1 = s(1, 2, 3, 2)
+    >>> s2 = s1.add(4)
+    >>> s3 = s1.remove(1)
+    >>> s1
+    pset([1, 2, 3])
+    >>> s2
+    pset([1, 2, 3, 4])
+    >>> s3
+    pset([2, 3])
+
+    # Full support for set operations
+    >>> s1 | s(3, 4, 5)
+    pset([1, 2, 3, 4, 5])
+    >>> s1 & s(3, 4, 5)
+    pset([3])
+    >>> s1 < s2
+    True
+    >>> s1 < s(3, 4, 5)
+    False
+
+.. _PRecord:
+
+PRecord
+~~~~~~~
+A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
+from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
+access using subscript notation.
+
+.. code:: python
+
+    >>> from pyrsistent import PRecord, field
+    >>> class ARecord(PRecord):
+    ...     x = field()
+    ...
+    >>> r = ARecord(x=3)
+    >>> r
+    ARecord(x=3)
+    >>> r.x
+    3
+    >>> r.set(x=2)
+    ARecord(x=2)
+    >>> r.set(y=2)
+    Traceback (most recent call last):
+    AttributeError: 'y' is not among the specified fields for ARecord
+
+Type information
+****************
+It is possible to add type information to the record to enforce type checks. Multiple allowed types can be specified
+by providing an iterable of types.
+
+.. code:: python
+
+    >>> class BRecord(PRecord):
+    ...     x = field(type=int)
+    ...     y = field(type=(int, type(None)))
+    ...
+    >>> BRecord(x=3, y=None)
+    BRecord(y=None, x=3)
+    >>> BRecord(x=3.0)
+    Traceback (most recent call last):
+    PTypeError: Invalid type for field BRecord.x, was float
+
+
+Custom types (classes) that are iterable should be wrapped in a tuple to prevent their
+members being added to the set of valid types.  Although Enums in particular are now 
+supported without wrapping, see #83 for more information.
+
+Mandatory fields
+****************
+Fields are not mandatory by default but can be specified as such. If fields are missing an
+*InvariantException* will be thrown which contains information about the missing fields.
+
+.. code:: python
+
+    >>> from pyrsistent import InvariantException
+    >>> class CRecord(PRecord):
+    ...     x = field(mandatory=True)
+    ...
+    >>> r = CRecord(x=3)
+    >>> try:
+    ...    r.discard('x')
+    ... except InvariantException as e:
+    ...    print(e.missing_fields)
+    ...
+    ('CRecord.x',)
+
+Invariants
+**********
+It is possible to add invariants that must hold when evolving the record. Invariants can be
+specified on both field and record level. If invariants fail an *InvariantException* will be
+thrown which contains information about the failing invariants. An invariant function should
+return a tuple consisting of a boolean that tells if the invariant holds or not and an object
+describing the invariant. This object can later be used to identify which invariant that failed.
+
+The global invariant function is only executed if all field invariants hold.
+
+Global invariants are inherited to subclasses.
+
+.. code:: python
+
+    >>> class RestrictedVector(PRecord):
+    ...     __invariant__ = lambda r: (r.y >= r.x, 'x larger than y')
+    ...     x = field(invariant=lambda x: (x > 0, 'x negative'))
+    ...     y = field(invariant=lambda y: (y > 0, 'y negative'))
+    ...
+    >>> r = RestrictedVector(y=3, x=2)
+    >>> try:
+    ...    r.set(x=-1, y=-2)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    ('y negative', 'x negative')
+    >>> try:
+    ...    r.set(x=2, y=1)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    ('x larger than y',)
+
+Invariants may also contain multiple assertions. For those cases the invariant function should
+return a tuple of invariant tuples as described above. This structure is reflected in the
+invariant_errors attribute of the exception which will contain tuples with data from all failed
+invariants. Eg:
+
+.. code:: python
+
+    >>> class EvenX(PRecord):
+    ...     x = field(invariant=lambda x: ((x > 0, 'x negative'), (x % 2 == 0, 'x odd')))
+    ...
+    >>> try:
+    ...    EvenX(x=-1)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    (('x negative', 'x odd'),)
+
+
+Factories
+*********
+It's possible to specify factory functions for fields. The factory function receives whatever
+is supplied as field value and the actual returned by the factory is assigned to the field
+given that any type and invariant checks hold.
+PRecords have a default factory specified as a static function on the class, create(). It takes
+a *Mapping* as argument and returns an instance of the specific record.
+If a record has fields of type PRecord the create() method of that record will
+be called to create the "sub record" if no factory has explicitly been specified to override
+this behaviour.
+
+.. code:: python
+
+    >>> class DRecord(PRecord):
+    ...     x = field(factory=int)
+    ...
+    >>> class ERecord(PRecord):
+    ...     d = field(type=DRecord)
+    ...
+    >>> ERecord.create({'d': {'x': '1'}})
+    ERecord(d=DRecord(x=1))
+
+Collection fields
+*****************
+It is also possible to have fields with ``pyrsistent`` collections.
+
+.. code:: python
+
+   >>> from pyrsistent import pset_field, pmap_field, pvector_field
+   >>> class MultiRecord(PRecord):
+   ...     set_of_ints = pset_field(int)
+   ...     map_int_to_str = pmap_field(int, str)
+   ...     vector_of_strs = pvector_field(str)
+   ...
+	
+Serialization
+*************
+PRecords support serialization back to dicts. Default serialization will take keys and values
+"as is" and output them into a dict. It is possible to specify custom serialization functions
+to take care of fields that require special treatment.
+
+.. code:: python
+
+    >>> from datetime import date
+    >>> class Person(PRecord):
+    ...     name = field(type=unicode)
+    ...     birth_date = field(type=date,
+    ...                        serializer=lambda format, d: d.strftime(format['date']))
+    ...
+    >>> john = Person(name=u'John', birth_date=date(1985, 10, 21))
+    >>> john.serialize({'date': '%Y-%m-%d'})
+    {'birth_date': '1985-10-21', 'name': u'John'}
+
+
+.. _instar: https://github.com/boxed/instar/
+
+.. _PClass:
+
+PClass
+~~~~~~
+A PClass is a python class with a fixed set of specified fields. PClasses are declared as python classes inheriting
+from PClass. It is defined the same way that PRecords are and behaves like a PRecord in all aspects except that it
+is not a PMap and hence not a collection but rather a plain Python object.
+
+.. code:: python
+
+    >>> from pyrsistent import PClass, field
+    >>> class AClass(PClass):
+    ...     x = field()
+    ...
+    >>> a = AClass(x=3)
+    >>> a
+    AClass(x=3)
+    >>> a.x
+    3
+
+
+Checked collections
+~~~~~~~~~~~~~~~~~~~
+Checked collections currently come in three flavors: CheckedPVector, CheckedPMap and CheckedPSet.
+
+.. code:: python
+
+    >>> from pyrsistent import CheckedPVector, CheckedPMap, CheckedPSet, thaw
+    >>> class Positives(CheckedPSet):
+    ...     __type__ = (long, int)
+    ...     __invariant__ = lambda n: (n >= 0, 'Negative')
+    ...
+    >>> class Lottery(PRecord):
+    ...     name = field(type=str)
+    ...     numbers = field(type=Positives, invariant=lambda p: (len(p) > 0, 'No numbers'))
+    ...
+    >>> class Lotteries(CheckedPVector):
+    ...     __type__ = Lottery
+    ...
+    >>> class LotteriesByDate(CheckedPMap):
+    ...     __key_type__ = date
+    ...     __value_type__ = Lotteries
+    ...
+    >>> lotteries = LotteriesByDate.create({date(2015, 2, 15): [{'name': 'SuperLotto', 'numbers': {1, 2, 3}},
+    ...                                                         {'name': 'MegaLotto',  'numbers': {4, 5, 6}}],
+    ...                                     date(2015, 2, 16): [{'name': 'SuperLotto', 'numbers': {3, 2, 1}},
+    ...                                                         {'name': 'MegaLotto',  'numbers': {6, 5, 4}}]})
+    >>> lotteries
+    LotteriesByDate({datetime.date(2015, 2, 15): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')]), datetime.date(2015, 2, 16): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])})
+
+    # The checked versions support all operations that the corresponding
+    # unchecked types do
+    >>> lottery_0215 = lotteries[date(2015, 2, 15)]
+    >>> lottery_0215.transform([0, 'name'], 'SuperDuperLotto')
+    Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperDuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])
+
+    # But also makes asserts that types and invariants hold
+    >>> lottery_0215.transform([0, 'name'], 999)
+    Traceback (most recent call last):
+    PTypeError: Invalid type for field Lottery.name, was int
+
+    >>> lottery_0215.transform([0, 'numbers'], set())
+    Traceback (most recent call last):
+    InvariantException: Field invariant failed
+
+    # They can be converted back to python built ins with either thaw()
+    # or serialize() (which provides possibilities to customize serialization)
+    >>> thaw(lottery_0215)
+    [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+    >>> lottery_0215.serialize()
+    [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+
+.. _transformations:
+
+Transformations
+~~~~~~~~~~~~~~~
+Transformations are inspired by the cool library instar_ for Clojure. They let you evolve PMaps and PVectors
+with arbitrarily deep/complex nesting using simple syntax and flexible matching syntax.
+
+The first argument to transformation is the path that points out the value to transform. The
+second is the transformation to perform. If the transformation is callable it will be applied
+to the value(s) matching the path. The path may also contain callables. In that case they are
+treated as matchers. If the matcher returns True for a specific key it is considered for transformation.
+
+.. code:: python
+
+    # Basic examples
+    >>> from pyrsistent import inc, freeze, thaw, rex, ny, discard
+    >>> v1 = freeze([1, 2, 3, 4, 5])
+    >>> v1.transform([2], inc)
+    pvector([1, 2, 4, 4, 5])
+    >>> v1.transform([lambda ix: 0 < ix < 4], 8)
+    pvector([1, 8, 8, 8, 5])
+    >>> v1.transform([lambda ix, v: ix == 0 or v == 5], 0)
+    pvector([0, 2, 3, 4, 0])
+
+    # The (a)ny matcher can be used to match anything
+    >>> v1.transform([ny], 8)
+    pvector([8, 8, 8, 8, 8])
+
+    # Regular expressions can be used for matching
+    >>> scores = freeze({'John': 12, 'Joseph': 34, 'Sara': 23})
+    >>> scores.transform([rex('^Jo')], 0)
+    pmap({'Joseph': 0, 'Sara': 23, 'John': 0})
+
+    # Transformations can be done on arbitrarily deep structures
+    >>> news_paper = freeze({'articles': [{'author': 'Sara', 'content': 'A short article'},
+    ...                                   {'author': 'Steve', 'content': 'A slightly longer article'}],
+    ...                      'weather': {'temperature': '11C', 'wind': '5m/s'}})
+    >>> short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:25] + '...' if len(c) > 25 else c)
+    >>> very_short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:15] + '...' if len(c) > 15 else c)
+    >>> very_short_news.articles[0].content
+    'A short article'
+    >>> very_short_news.articles[1].content
+    'A slightly long...'
+
+    # When nothing has been transformed the original data structure is kept
+    >>> short_news is news_paper
+    True
+    >>> very_short_news is news_paper
+    False
+    >>> very_short_news.articles[0] is news_paper.articles[0]
+    True
+
+    # There is a special transformation that can be used to discard elements. Also
+    # multiple transformations can be applied in one call
+    >>> thaw(news_paper.transform(['weather'], discard, ['articles', ny, 'content'], discard))
+    {'articles': [{'author': 'Sara'}, {'author': 'Steve'}]}
+
+Evolvers
+~~~~~~~~
+PVector, PMap and PSet all have support for a concept dubbed *evolvers*. An evolver acts like a mutable
+view of the underlying persistent data structure with "transaction like" semantics. No updates of the original
+data structure is ever performed, it is still fully immutable.
+
+The evolvers have a very limited API by design to discourage excessive, and inappropriate, usage as that would
+take us down the mutable road. In principle only basic mutation and element access functions are supported.
+Check out the documentation_ of each data structure for specific examples.
+
+Examples of when you may want to use an evolver instead of working directly with the data structure include:
+
+* Multiple updates are done to the same data structure and the intermediate results are of no
+  interest. In this case using an evolver may be a more efficient and easier to work with.
+* You need to pass a vector into a legacy function or a function that you have no control
+  over which performs in place mutations. In this case pass an evolver instance
+  instead and then create a new pvector from the evolver once the function returns.
+
+.. code:: python
+
+    >>> from pyrsistent import v
+
+    # In place mutation as when working with the built in counterpart
+    >>> v1 = v(1, 2, 3)
+    >>> e = v1.evolver()
+    >>> e[1] = 22
+    >>> e = e.append(4)
+    >>> e = e.extend([5, 6])
+    >>> e[5] += 1
+    >>> len(e)
+    6
+
+    # The evolver is considered *dirty* when it contains changes compared to the underlying vector
+    >>> e.is_dirty()
+    True
+
+    # But the underlying pvector still remains untouched
+    >>> v1
+    pvector([1, 2, 3])
+
+    # Once satisfied with the updates you can produce a new pvector containing the updates.
+    # The new pvector will share data with the original pvector in the same way that would have
+    # been done if only using operations on the pvector.
+    >>> v2 = e.persistent()
+    >>> v2
+    pvector([1, 22, 3, 4, 5, 7])
+
+    # The evolver is now no longer considered *dirty* as it contains no differences compared to the
+    # pvector just produced.
+    >>> e.is_dirty()
+    False
+
+    # You may continue to work with the same evolver without affecting the content of v2
+    >>> e[0] = 11
+
+    # Or create a new evolver from v2. The two evolvers can be updated independently but will both
+    # share data with v2 where possible.
+    >>> e2 = v2.evolver()
+    >>> e2[0] = 1111
+    >>> e.persistent()
+    pvector([11, 22, 3, 4, 5, 7])
+    >>> e2.persistent()
+    pvector([1111, 22, 3, 4, 5, 7])
+
+.. _freeze:
+.. _thaw:
+
+freeze and thaw
+~~~~~~~~~~~~~~~
+These functions are great when your cozy immutable world has to interact with the evil mutable world outside.
+
+.. code:: python
+
+    >>> from pyrsistent import freeze, thaw, v, m
+    >>> freeze([1, {'a': 3}])
+    pvector([1, pmap({'a': 3})])
+    >>> thaw(v(1, m(a=3)))
+    [1, {'a': 3}]
+
+Compatibility
+-------------
+
+Pyrsistent is developed and tested on Python 2.7, 3.5, 3.6, 3.7 and PyPy (Python 2 and 3 compatible). It will most
+likely work on all other versions >= 3.4 but no guarantees are given. :)
+
+Compatibility issues
+~~~~~~~~~~~~~~~~~~~~
+
+.. _27: https://github.com/tobgu/pyrsistent/issues/27
+
+There is currently one known compatibility issue when comparing built in sets and frozensets to PSets as discussed in 27_.
+It affects python 2 versions < 2.7.8 and python 3 versions < 3.4.0 and is due to a bug described in
+http://bugs.python.org/issue8743.
+
+Comparisons will fail or be incorrect when using the set/frozenset as left hand side of the comparison. As a workaround
+you need to either upgrade Python to a more recent version, avoid comparing sets/frozensets with PSets or always make
+sure to convert both sides of the comparison to the same type before performing the comparison.
+
+Performance
+-----------
+
+Pyrsistent is developed with performance in mind. Still, while some operations are nearly on par with their built in, 
+mutable, counterparts in terms of speed, other operations are slower. In the cases where attempts at
+optimizations have been done, speed has generally been valued over space.
+
+Pyrsistent comes with two API compatible flavors of PVector (on which PMap and PSet are based), one pure Python 
+implementation and one implemented as a C extension. The latter generally being 2 - 20 times faster than the former.
+The C extension will be used automatically when possible.
+
+The pure python implementation is fully PyPy compatible. Running it under PyPy speeds operations up considerably if 
+the structures are used heavily (if JITed), for some cases the performance is almost on par with the built in counterparts.
+
+Type hints
+----------
+
+PEP 561 style type hints for use with mypy and various editors are available for most types and functions in pyrsistent.
+
+Type classes for annotating your own code with pyrsistent types are also available under pyrsistent.typing.
+
+Installation
+------------
+
+pip install pyrsistent
+
+Documentation
+-------------
+
+Available at http://pyrsistent.readthedocs.org/
+
+Brief presentation available at http://slides.com/tobiasgustafsson/immutability-and-python/
+
+Contributors
+------------
+
+Tobias Gustafsson https://github.com/tobgu
+
+Christopher Armstrong https://github.com/radix
+
+Anders Hovmöller https://github.com/boxed
+
+Itamar Turner-Trauring https://github.com/itamarst
+
+Jonathan Lange https://github.com/jml
+
+Richard Futrell https://github.com/Futrell
+
+Jakob Hollenstein https://github.com/jkbjh
+
+David Honour https://github.com/foolswood
+
+David R. MacIver https://github.com/DRMacIver
+
+Marcus Ewert https://github.com/sarum90
+
+Jean-Paul Calderone https://github.com/exarkun
+
+Douglas Treadwell https://github.com/douglas-treadwell
+
+Travis Parker https://github.com/teepark
+
+Julian Berman https://github.com/Julian
+
+Dennis Tomas https://github.com/dtomas
+
+Neil Vyas https://github.com/neilvyas
+
+doozr https://github.com/doozr
+
+Kamil Galuszka https://github.com/galuszkak
+
+Tsuyoshi Hombashi https://github.com/thombashi
+
+nattofriends https://github.com/nattofriends
+
+agberk https://github.com/agberk
+
+Waleed Khan https://github.com/arxanas
+
+Jean-Louis Fuchs https://github.com/ganwell
+
+Carlos Corbacho https://github.com/ccorbacho
+
+Felix Yan https://github.com/felixonmars
+
+benrg https://github.com/benrg
+
+Jere Lahelma https://github.com/je-l
+
+Max Taggart https://github.com/MaxTaggart
+
+Vincent Philippon https://github.com/vphilippon
+
+Semen Zhydenko https://github.com/ss18
+
+Till Varoquaux  https://github.com/till-varoquaux
+
+Michal Kowalik https://github.com/michalvi
+
+ossdev07 https://github.com/ossdev07
+
+Kerry Olesen https://github.com/qhesz
+
+johnthagen https://github.com/johnthagen
+
+Contributing
+------------
+
+Want to contribute? That's great! If you experience problems please log them on GitHub. If you want to contribute code,
+please fork the repository and submit a pull request.
+
+Run tests
+~~~~~~~~~
+.. _tox: https://tox.readthedocs.io/en/latest/
+
+Tests can be executed using tox_.
+
+Install tox: ``pip install tox``
+
+Run test for Python 2.7: ``tox -epy27``
+
+Release
+~~~~~~~
+* Update CHANGES.txt
+* Update README with any new contributors and potential info needed.
+* Update _pyrsistent_version.py
+* python setup.py sdist upload
+* Commit and tag with new version: git add -u . && git commit -m 'Prepare version vX.Y.Z' && git tag -a vX.Y.Z -m 'vX.Y.Z'
+* Push commit and tags: git push && git push --tags
+
+Project status
+--------------
+Pyrsistent can be considered stable and mature (who knows, there may even be a 1.0 some day :-)). The project is
+maintained, bugs fixed, PRs reviewed and merged and new releases made. I currently do not have time for development
+of new features or functionality which I don't have use for myself. I'm more than happy to take PRs for new
+functionality though!
+
+There are a bunch of issues marked with ``enhancement`` and ``help wanted`` that contain requests for new functionality
+that would be nice to include. The level of difficulty and extend of the issues varies, please reach out to me if you're
+interested in working on any of them.
+
+If you feel that you have a grand master plan for where you would like Pyrsistent to go and have the time to put into
+it please don't hesitate to discuss this with me and submit PRs for it. If all goes well I'd be more than happy to add
+additional maintainers to the project!
diff --git a/third_party/python/pyrsistent/README.rst b/third_party/python/pyrsistent/README.rst
new file mode 100644
index 0000000000..a4c24e49bd
--- /dev/null
+++ b/third_party/python/pyrsistent/README.rst
@@ -0,0 +1,725 @@
+Pyrsistent
+==========
+.. image:: https://travis-ci.org/tobgu/pyrsistent.png?branch=master
+    :target: https://travis-ci.org/tobgu/pyrsistent
+
+.. image:: https://badge.fury.io/py/pyrsistent.svg
+    :target: https://badge.fury.io/py/pyrsistent
+
+.. image:: https://coveralls.io/repos/tobgu/pyrsistent/badge.svg?branch=master&service=github
+    :target: https://coveralls.io/github/tobgu/pyrsistent?branch=master
+
+
+.. _Pyrthon: https://www.github.com/tobgu/pyrthon/
+
+Pyrsistent is a number of persistent collections (by some referred to as functional data structures). Persistent in 
+the sense that they are immutable.
+
+All methods on a data structure that would normally mutate it instead return a new copy of the structure containing the
+requested updates. The original structure is left untouched.
+
+This will simplify the reasoning about what a program does since no hidden side effects ever can take place to these
+data structures. You can rest assured that the object you hold a reference to will remain the same throughout its
+lifetime and need not worry that somewhere five stack levels below you in the darkest corner of your application
+someone has decided to remove that element that you expected to be there.
+
+Pyrsistent is influenced by persistent data structures such as those found in the standard library of Clojure. The
+data structures are designed to share common elements through path copying.
+It aims at taking these concepts and make them as pythonic as possible so that they can be easily integrated into any python
+program without hassle.
+
+If you want to go all in on persistent data structures and use literal syntax to define them in your code rather
+than function calls check out Pyrthon_.
+
+Examples
+--------
+.. _Sequence: collections_
+.. _Hashable: collections_
+.. _Mapping: collections_
+.. _Mappings: collections_
+.. _Set: collections_
+.. _collections: https://docs.python.org/3/library/collections.abc.html
+.. _documentation: http://pyrsistent.readthedocs.org/
+
+The collection types and key features currently implemented are:
+
+* PVector_, similar to a python list
+* PMap_, similar to dict
+* PSet_, similar to set
+* PRecord_, a PMap on steroids with fixed fields, optional type and invariant checking and much more
+* PClass_, a Python class fixed fields, optional type and invariant checking and much more
+* `Checked collections`_, PVector, PMap and PSet with optional type and invariance checks and more
+* PBag, similar to collections.Counter
+* PList, a classic singly linked list
+* PDeque, similar to collections.deque
+* Immutable object type (immutable) built on the named tuple
+* freeze_ and thaw_ functions to convert between pythons standard collections and pyrsistent collections.
+* Flexible transformations_ of arbitrarily complex structures built from PMaps and PVectors.
+
+Below are examples of common usage patterns for some of the structures and features. More information and
+full documentation for all data structures is available in the documentation_.
+
+.. _PVector:
+
+PVector
+~~~~~~~
+With full support for the Sequence_ protocol PVector is meant as a drop in replacement to the built in list from a readers
+point of view. Write operations of course differ since no in place mutation is done but naming should be in line
+with corresponding operations on the built in list.
+
+Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+
+Appends are amortized O(1). Random access and insert is log32(n) where n is the size of the vector.
+
+.. code:: python
+
+    >>> from pyrsistent import v, pvector
+
+    # No mutation of vectors once created, instead they
+    # are "evolved" leaving the original untouched
+    >>> v1 = v(1, 2, 3)
+    >>> v2 = v1.append(4)
+    >>> v3 = v2.set(1, 5)
+    >>> v1
+    pvector([1, 2, 3])
+    >>> v2
+    pvector([1, 2, 3, 4])
+    >>> v3
+    pvector([1, 5, 3, 4])
+
+    # Random access and slicing
+    >>> v3[1]
+    5
+    >>> v3[1:3]
+    pvector([5, 3])
+
+    # Iteration
+    >>> list(x + 1 for x in v3)
+    [2, 6, 4, 5]
+    >>> pvector(2 * x for x in range(3))
+    pvector([0, 2, 4])
+
+.. _PMap:
+
+PMap
+~~~~
+With full support for the Mapping_ protocol PMap is meant as a drop in replacement to the built in dict from a readers point
+of view. Support for the Hashable_ protocol also means that it can be used as key in other Mappings_.
+
+Random access and insert is log32(n) where n is the size of the map.
+
+.. code:: python
+
+    >>> from pyrsistent import m, pmap, v
+
+    # No mutation of maps once created, instead they are
+    # "evolved" leaving the original untouched
+    >>> m1 = m(a=1, b=2)
+    >>> m2 = m1.set('c', 3)
+    >>> m3 = m2.set('a', 5)
+    >>> m1
+    pmap({'a': 1, 'b': 2})
+    >>> m2
+    pmap({'a': 1, 'c': 3, 'b': 2})
+    >>> m3
+    pmap({'a': 5, 'c': 3, 'b': 2})
+    >>> m3['a']
+    5
+
+    # Evolution of nested persistent structures
+    >>> m4 = m(a=5, b=6, c=v(1, 2))
+    >>> m4.transform(('c', 1), 17)
+    pmap({'a': 5, 'c': pvector([1, 17]), 'b': 6})
+    >>> m5 = m(a=1, b=2)
+
+    # Evolve by merging with other mappings
+    >>> m5.update(m(a=2, c=3), {'a': 17, 'd': 35})
+    pmap({'a': 17, 'c': 3, 'b': 2, 'd': 35})
+    >>> pmap({'x': 1, 'y': 2}) + pmap({'y': 3, 'z': 4})
+    pmap({'y': 3, 'x': 1, 'z': 4})
+
+    # Dict-like methods to convert to list and iterate
+    >>> m3.items()
+    pvector([('a', 5), ('c', 3), ('b', 2)])
+    >>> list(m3)
+    ['a', 'c', 'b']
+
+.. _PSet:
+
+PSet
+~~~~
+With full support for the Set_ protocol PSet is meant as a drop in replacement to the built in set from a readers point
+of view. Support for the Hashable_ protocol also means that it can be used as key in Mappings_.
+
+Random access and insert is log32(n) where n is the size of the set.
+
+.. code:: python
+
+    >>> from pyrsistent import s
+
+    # No mutation of sets once created, you know the story...
+    >>> s1 = s(1, 2, 3, 2)
+    >>> s2 = s1.add(4)
+    >>> s3 = s1.remove(1)
+    >>> s1
+    pset([1, 2, 3])
+    >>> s2
+    pset([1, 2, 3, 4])
+    >>> s3
+    pset([2, 3])
+
+    # Full support for set operations
+    >>> s1 | s(3, 4, 5)
+    pset([1, 2, 3, 4, 5])
+    >>> s1 & s(3, 4, 5)
+    pset([3])
+    >>> s1 < s2
+    True
+    >>> s1 < s(3, 4, 5)
+    False
+
+.. _PRecord:
+
+PRecord
+~~~~~~~
+A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
+from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
+access using subscript notation.
+
+.. code:: python
+
+    >>> from pyrsistent import PRecord, field
+    >>> class ARecord(PRecord):
+    ...     x = field()
+    ...
+    >>> r = ARecord(x=3)
+    >>> r
+    ARecord(x=3)
+    >>> r.x
+    3
+    >>> r.set(x=2)
+    ARecord(x=2)
+    >>> r.set(y=2)
+    Traceback (most recent call last):
+    AttributeError: 'y' is not among the specified fields for ARecord
+
+Type information
+****************
+It is possible to add type information to the record to enforce type checks. Multiple allowed types can be specified
+by providing an iterable of types.
+
+.. code:: python
+
+    >>> class BRecord(PRecord):
+    ...     x = field(type=int)
+    ...     y = field(type=(int, type(None)))
+    ...
+    >>> BRecord(x=3, y=None)
+    BRecord(y=None, x=3)
+    >>> BRecord(x=3.0)
+    Traceback (most recent call last):
+    PTypeError: Invalid type for field BRecord.x, was float
+
+
+Custom types (classes) that are iterable should be wrapped in a tuple to prevent their
+members being added to the set of valid types.  Although Enums in particular are now 
+supported without wrapping, see #83 for more information.
+
+Mandatory fields
+****************
+Fields are not mandatory by default but can be specified as such. If fields are missing an
+*InvariantException* will be thrown which contains information about the missing fields.
+
+.. code:: python
+
+    >>> from pyrsistent import InvariantException
+    >>> class CRecord(PRecord):
+    ...     x = field(mandatory=True)
+    ...
+    >>> r = CRecord(x=3)
+    >>> try:
+    ...    r.discard('x')
+    ... except InvariantException as e:
+    ...    print(e.missing_fields)
+    ...
+    ('CRecord.x',)
+
+Invariants
+**********
+It is possible to add invariants that must hold when evolving the record. Invariants can be
+specified on both field and record level. If invariants fail an *InvariantException* will be
+thrown which contains information about the failing invariants. An invariant function should
+return a tuple consisting of a boolean that tells if the invariant holds or not and an object
+describing the invariant. This object can later be used to identify which invariant that failed.
+
+The global invariant function is only executed if all field invariants hold.
+
+Global invariants are inherited to subclasses.
+
+.. code:: python
+
+    >>> class RestrictedVector(PRecord):
+    ...     __invariant__ = lambda r: (r.y >= r.x, 'x larger than y')
+    ...     x = field(invariant=lambda x: (x > 0, 'x negative'))
+    ...     y = field(invariant=lambda y: (y > 0, 'y negative'))
+    ...
+    >>> r = RestrictedVector(y=3, x=2)
+    >>> try:
+    ...    r.set(x=-1, y=-2)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    ('y negative', 'x negative')
+    >>> try:
+    ...    r.set(x=2, y=1)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    ('x larger than y',)
+
+Invariants may also contain multiple assertions. For those cases the invariant function should
+return a tuple of invariant tuples as described above. This structure is reflected in the
+invariant_errors attribute of the exception which will contain tuples with data from all failed
+invariants. Eg:
+
+.. code:: python
+
+    >>> class EvenX(PRecord):
+    ...     x = field(invariant=lambda x: ((x > 0, 'x negative'), (x % 2 == 0, 'x odd')))
+    ...
+    >>> try:
+    ...    EvenX(x=-1)
+    ... except InvariantException as e:
+    ...    print(e.invariant_errors)
+    ...
+    (('x negative', 'x odd'),)
+
+
+Factories
+*********
+It's possible to specify factory functions for fields. The factory function receives whatever
+is supplied as field value and the actual returned by the factory is assigned to the field
+given that any type and invariant checks hold.
+PRecords have a default factory specified as a static function on the class, create(). It takes
+a *Mapping* as argument and returns an instance of the specific record.
+If a record has fields of type PRecord the create() method of that record will
+be called to create the "sub record" if no factory has explicitly been specified to override
+this behaviour.
+
+.. code:: python
+
+    >>> class DRecord(PRecord):
+    ...     x = field(factory=int)
+    ...
+    >>> class ERecord(PRecord):
+    ...     d = field(type=DRecord)
+    ...
+    >>> ERecord.create({'d': {'x': '1'}})
+    ERecord(d=DRecord(x=1))
+
+Collection fields
+*****************
+It is also possible to have fields with ``pyrsistent`` collections.
+
+.. code:: python
+
+   >>> from pyrsistent import pset_field, pmap_field, pvector_field
+   >>> class MultiRecord(PRecord):
+   ...     set_of_ints = pset_field(int)
+   ...     map_int_to_str = pmap_field(int, str)
+   ...     vector_of_strs = pvector_field(str)
+   ...
+	
+Serialization
+*************
+PRecords support serialization back to dicts. Default serialization will take keys and values
+"as is" and output them into a dict. It is possible to specify custom serialization functions
+to take care of fields that require special treatment.
+
+.. code:: python
+
+    >>> from datetime import date
+    >>> class Person(PRecord):
+    ...     name = field(type=unicode)
+    ...     birth_date = field(type=date,
+    ...                        serializer=lambda format, d: d.strftime(format['date']))
+    ...
+    >>> john = Person(name=u'John', birth_date=date(1985, 10, 21))
+    >>> john.serialize({'date': '%Y-%m-%d'})
+    {'birth_date': '1985-10-21', 'name': u'John'}
+
+
+.. _instar: https://github.com/boxed/instar/
+
+.. _PClass:
+
+PClass
+~~~~~~
+A PClass is a python class with a fixed set of specified fields. PClasses are declared as python classes inheriting
+from PClass. It is defined the same way that PRecords are and behaves like a PRecord in all aspects except that it
+is not a PMap and hence not a collection but rather a plain Python object.
+
+.. code:: python
+
+    >>> from pyrsistent import PClass, field
+    >>> class AClass(PClass):
+    ...     x = field()
+    ...
+    >>> a = AClass(x=3)
+    >>> a
+    AClass(x=3)
+    >>> a.x
+    3
+
+
+Checked collections
+~~~~~~~~~~~~~~~~~~~
+Checked collections currently come in three flavors: CheckedPVector, CheckedPMap and CheckedPSet.
+
+.. code:: python
+
+    >>> from pyrsistent import CheckedPVector, CheckedPMap, CheckedPSet, thaw
+    >>> class Positives(CheckedPSet):
+    ...     __type__ = (long, int)
+    ...     __invariant__ = lambda n: (n >= 0, 'Negative')
+    ...
+    >>> class Lottery(PRecord):
+    ...     name = field(type=str)
+    ...     numbers = field(type=Positives, invariant=lambda p: (len(p) > 0, 'No numbers'))
+    ...
+    >>> class Lotteries(CheckedPVector):
+    ...     __type__ = Lottery
+    ...
+    >>> class LotteriesByDate(CheckedPMap):
+    ...     __key_type__ = date
+    ...     __value_type__ = Lotteries
+    ...
+    >>> lotteries = LotteriesByDate.create({date(2015, 2, 15): [{'name': 'SuperLotto', 'numbers': {1, 2, 3}},
+    ...                                                         {'name': 'MegaLotto',  'numbers': {4, 5, 6}}],
+    ...                                     date(2015, 2, 16): [{'name': 'SuperLotto', 'numbers': {3, 2, 1}},
+    ...                                                         {'name': 'MegaLotto',  'numbers': {6, 5, 4}}]})
+    >>> lotteries
+    LotteriesByDate({datetime.date(2015, 2, 15): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')]), datetime.date(2015, 2, 16): Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])})
+
+    # The checked versions support all operations that the corresponding
+    # unchecked types do
+    >>> lottery_0215 = lotteries[date(2015, 2, 15)]
+    >>> lottery_0215.transform([0, 'name'], 'SuperDuperLotto')
+    Lotteries([Lottery(numbers=Positives([1, 2, 3]), name='SuperDuperLotto'), Lottery(numbers=Positives([4, 5, 6]), name='MegaLotto')])
+
+    # But also makes asserts that types and invariants hold
+    >>> lottery_0215.transform([0, 'name'], 999)
+    Traceback (most recent call last):
+    PTypeError: Invalid type for field Lottery.name, was int
+
+    >>> lottery_0215.transform([0, 'numbers'], set())
+    Traceback (most recent call last):
+    InvariantException: Field invariant failed
+
+    # They can be converted back to python built ins with either thaw()
+    # or serialize() (which provides possibilities to customize serialization)
+    >>> thaw(lottery_0215)
+    [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+    >>> lottery_0215.serialize()
+    [{'numbers': set([1, 2, 3]), 'name': 'SuperLotto'}, {'numbers': set([4, 5, 6]), 'name': 'MegaLotto'}]
+
+.. _transformations:
+
+Transformations
+~~~~~~~~~~~~~~~
+Transformations are inspired by the cool library instar_ for Clojure. They let you evolve PMaps and PVectors
+with arbitrarily deep/complex nesting using simple syntax and flexible matching syntax.
+
+The first argument to transformation is the path that points out the value to transform. The
+second is the transformation to perform. If the transformation is callable it will be applied
+to the value(s) matching the path. The path may also contain callables. In that case they are
+treated as matchers. If the matcher returns True for a specific key it is considered for transformation.
+
+.. code:: python
+
+    # Basic examples
+    >>> from pyrsistent import inc, freeze, thaw, rex, ny, discard
+    >>> v1 = freeze([1, 2, 3, 4, 5])
+    >>> v1.transform([2], inc)
+    pvector([1, 2, 4, 4, 5])
+    >>> v1.transform([lambda ix: 0 < ix < 4], 8)
+    pvector([1, 8, 8, 8, 5])
+    >>> v1.transform([lambda ix, v: ix == 0 or v == 5], 0)
+    pvector([0, 2, 3, 4, 0])
+
+    # The (a)ny matcher can be used to match anything
+    >>> v1.transform([ny], 8)
+    pvector([8, 8, 8, 8, 8])
+
+    # Regular expressions can be used for matching
+    >>> scores = freeze({'John': 12, 'Joseph': 34, 'Sara': 23})
+    >>> scores.transform([rex('^Jo')], 0)
+    pmap({'Joseph': 0, 'Sara': 23, 'John': 0})
+
+    # Transformations can be done on arbitrarily deep structures
+    >>> news_paper = freeze({'articles': [{'author': 'Sara', 'content': 'A short article'},
+    ...                                   {'author': 'Steve', 'content': 'A slightly longer article'}],
+    ...                      'weather': {'temperature': '11C', 'wind': '5m/s'}})
+    >>> short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:25] + '...' if len(c) > 25 else c)
+    >>> very_short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:15] + '...' if len(c) > 15 else c)
+    >>> very_short_news.articles[0].content
+    'A short article'
+    >>> very_short_news.articles[1].content
+    'A slightly long...'
+
+    # When nothing has been transformed the original data structure is kept
+    >>> short_news is news_paper
+    True
+    >>> very_short_news is news_paper
+    False
+    >>> very_short_news.articles[0] is news_paper.articles[0]
+    True
+
+    # There is a special transformation that can be used to discard elements. Also
+    # multiple transformations can be applied in one call
+    >>> thaw(news_paper.transform(['weather'], discard, ['articles', ny, 'content'], discard))
+    {'articles': [{'author': 'Sara'}, {'author': 'Steve'}]}
+
+Evolvers
+~~~~~~~~
+PVector, PMap and PSet all have support for a concept dubbed *evolvers*. An evolver acts like a mutable
+view of the underlying persistent data structure with "transaction like" semantics. No updates of the original
+data structure is ever performed, it is still fully immutable.
+
+The evolvers have a very limited API by design to discourage excessive, and inappropriate, usage as that would
+take us down the mutable road. In principle only basic mutation and element access functions are supported.
+Check out the documentation_ of each data structure for specific examples.
+
+Examples of when you may want to use an evolver instead of working directly with the data structure include:
+
+* Multiple updates are done to the same data structure and the intermediate results are of no
+  interest. In this case using an evolver may be a more efficient and easier to work with.
+* You need to pass a vector into a legacy function or a function that you have no control
+  over which performs in place mutations. In this case pass an evolver instance
+  instead and then create a new pvector from the evolver once the function returns.
+
+.. code:: python
+
+    >>> from pyrsistent import v
+
+    # In place mutation as when working with the built in counterpart
+    >>> v1 = v(1, 2, 3)
+    >>> e = v1.evolver()
+    >>> e[1] = 22
+    >>> e = e.append(4)
+    >>> e = e.extend([5, 6])
+    >>> e[5] += 1
+    >>> len(e)
+    6
+
+    # The evolver is considered *dirty* when it contains changes compared to the underlying vector
+    >>> e.is_dirty()
+    True
+
+    # But the underlying pvector still remains untouched
+    >>> v1
+    pvector([1, 2, 3])
+
+    # Once satisfied with the updates you can produce a new pvector containing the updates.
+    # The new pvector will share data with the original pvector in the same way that would have
+    # been done if only using operations on the pvector.
+    >>> v2 = e.persistent()
+    >>> v2
+    pvector([1, 22, 3, 4, 5, 7])
+
+    # The evolver is now no longer considered *dirty* as it contains no differences compared to the
+    # pvector just produced.
+    >>> e.is_dirty()
+    False
+
+    # You may continue to work with the same evolver without affecting the content of v2
+    >>> e[0] = 11
+
+    # Or create a new evolver from v2. The two evolvers can be updated independently but will both
+    # share data with v2 where possible.
+    >>> e2 = v2.evolver()
+    >>> e2[0] = 1111
+    >>> e.persistent()
+    pvector([11, 22, 3, 4, 5, 7])
+    >>> e2.persistent()
+    pvector([1111, 22, 3, 4, 5, 7])
+
+.. _freeze:
+.. _thaw:
+
+freeze and thaw
+~~~~~~~~~~~~~~~
+These functions are great when your cozy immutable world has to interact with the evil mutable world outside.
+
+.. code:: python
+
+    >>> from pyrsistent import freeze, thaw, v, m
+    >>> freeze([1, {'a': 3}])
+    pvector([1, pmap({'a': 3})])
+    >>> thaw(v(1, m(a=3)))
+    [1, {'a': 3}]
+
+Compatibility
+-------------
+
+Pyrsistent is developed and tested on Python 2.7, 3.5, 3.6, 3.7 and PyPy (Python 2 and 3 compatible). It will most
+likely work on all other versions >= 3.4 but no guarantees are given. :)
+
+Compatibility issues
+~~~~~~~~~~~~~~~~~~~~
+
+.. _27: https://github.com/tobgu/pyrsistent/issues/27
+
+There is currently one known compatibility issue when comparing built in sets and frozensets to PSets as discussed in 27_.
+It affects python 2 versions < 2.7.8 and python 3 versions < 3.4.0 and is due to a bug described in
+http://bugs.python.org/issue8743.
+
+Comparisons will fail or be incorrect when using the set/frozenset as left hand side of the comparison. As a workaround
+you need to either upgrade Python to a more recent version, avoid comparing sets/frozensets with PSets or always make
+sure to convert both sides of the comparison to the same type before performing the comparison.
+
+Performance
+-----------
+
+Pyrsistent is developed with performance in mind. Still, while some operations are nearly on par with their built in, 
+mutable, counterparts in terms of speed, other operations are slower. In the cases where attempts at
+optimizations have been done, speed has generally been valued over space.
+
+Pyrsistent comes with two API compatible flavors of PVector (on which PMap and PSet are based), one pure Python 
+implementation and one implemented as a C extension. The latter generally being 2 - 20 times faster than the former.
+The C extension will be used automatically when possible.
+
+The pure python implementation is fully PyPy compatible. Running it under PyPy speeds operations up considerably if 
+the structures are used heavily (if JITed), for some cases the performance is almost on par with the built in counterparts.
+
+Type hints
+----------
+
+PEP 561 style type hints for use with mypy and various editors are available for most types and functions in pyrsistent.
+
+Type classes for annotating your own code with pyrsistent types are also available under pyrsistent.typing.
+
+Installation
+------------
+
+pip install pyrsistent
+
+Documentation
+-------------
+
+Available at http://pyrsistent.readthedocs.org/
+
+Brief presentation available at http://slides.com/tobiasgustafsson/immutability-and-python/
+
+Contributors
+------------
+
+Tobias Gustafsson https://github.com/tobgu
+
+Christopher Armstrong https://github.com/radix
+
+Anders Hovmöller https://github.com/boxed
+
+Itamar Turner-Trauring https://github.com/itamarst
+
+Jonathan Lange https://github.com/jml
+
+Richard Futrell https://github.com/Futrell
+
+Jakob Hollenstein https://github.com/jkbjh
+
+David Honour https://github.com/foolswood
+
+David R. MacIver https://github.com/DRMacIver
+
+Marcus Ewert https://github.com/sarum90
+
+Jean-Paul Calderone https://github.com/exarkun
+
+Douglas Treadwell https://github.com/douglas-treadwell
+
+Travis Parker https://github.com/teepark
+
+Julian Berman https://github.com/Julian
+
+Dennis Tomas https://github.com/dtomas
+
+Neil Vyas https://github.com/neilvyas
+
+doozr https://github.com/doozr
+
+Kamil Galuszka https://github.com/galuszkak
+
+Tsuyoshi Hombashi https://github.com/thombashi
+
+nattofriends https://github.com/nattofriends
+
+agberk https://github.com/agberk
+
+Waleed Khan https://github.com/arxanas
+
+Jean-Louis Fuchs https://github.com/ganwell
+
+Carlos Corbacho https://github.com/ccorbacho
+
+Felix Yan https://github.com/felixonmars
+
+benrg https://github.com/benrg
+
+Jere Lahelma https://github.com/je-l
+
+Max Taggart https://github.com/MaxTaggart
+
+Vincent Philippon https://github.com/vphilippon
+
+Semen Zhydenko https://github.com/ss18
+
+Till Varoquaux  https://github.com/till-varoquaux
+
+Michal Kowalik https://github.com/michalvi
+
+ossdev07 https://github.com/ossdev07
+
+Kerry Olesen https://github.com/qhesz
+
+johnthagen https://github.com/johnthagen
+
+Contributing
+------------
+
+Want to contribute? That's great! If you experience problems please log them on GitHub. If you want to contribute code,
+please fork the repository and submit a pull request.
+
+Run tests
+~~~~~~~~~
+.. _tox: https://tox.readthedocs.io/en/latest/
+
+Tests can be executed using tox_.
+
+Install tox: ``pip install tox``
+
+Run test for Python 2.7: ``tox -epy27``
+
+Release
+~~~~~~~
+* Update CHANGES.txt
+* Update README with any new contributors and potential info needed.
+* Update _pyrsistent_version.py
+* python setup.py sdist upload
+* Commit and tag with new version: git add -u . && git commit -m 'Prepare version vX.Y.Z' && git tag -a vX.Y.Z -m 'vX.Y.Z'
+* Push commit and tags: git push && git push --tags
+
+Project status
+--------------
+Pyrsistent can be considered stable and mature (who knows, there may even be a 1.0 some day :-)). The project is
+maintained, bugs fixed, PRs reviewed and merged and new releases made. I currently do not have time for development
+of new features or functionality which I don't have use for myself. I'm more than happy to take PRs for new
+functionality though!
+
+There are a bunch of issues marked with ``enhancement`` and ``help wanted`` that contain requests for new functionality
+that would be nice to include. The level of difficulty and extend of the issues varies, please reach out to me if you're
+interested in working on any of them.
+
+If you feel that you have a grand master plan for where you would like Pyrsistent to go and have the time to put into
+it please don't hesitate to discuss this with me and submit PRs for it. If all goes well I'd be more than happy to add
+additional maintainers to the project!
diff --git a/third_party/python/pyrsistent/_pyrsistent_version.py b/third_party/python/pyrsistent/_pyrsistent_version.py
new file mode 100644
index 0000000000..8911e95ca7
--- /dev/null
+++ b/third_party/python/pyrsistent/_pyrsistent_version.py
@@ -0,0 +1 @@
+__version__ = '0.16.0'
diff --git a/third_party/python/pyrsistent/pvectorcmodule.c b/third_party/python/pyrsistent/pvectorcmodule.c
new file mode 100644
index 0000000000..11a5bd6411
--- /dev/null
+++ b/third_party/python/pyrsistent/pvectorcmodule.c
@@ -0,0 +1,1642 @@
+#include <Python.h>
+#include <structmember.h>
+
+/*
+Persistent/Immutable/Functional vector and helper types. 
+
+Please note that they are anything but immutable at this level since
+there is a whole lot of reference counting going on. That's the way
+CPython works though and the GIL makes them appear immutable.
+
+To the programmer using them from Python they appear immutable and
+behave immutably at least.
+
+Naming conventions
+------------------
+initpyrsistentc - This is the method that initializes the whole module
+pyrsistent_* -    Methods part of the interface
+<typename>_* -    Instance methods of types. For examle PVector_append(...)
+
+All other methods are camel cased without prefix. All methods are static, none should
+require to be exposed outside of this module. 
+*/
+
+#define SHIFT 5
+#define BRANCH_FACTOR (1 << SHIFT)
+#define BIT_MASK (BRANCH_FACTOR - 1)
+
+static PyTypeObject PVectorType;
+static PyTypeObject PVectorEvolverType;
+
+typedef struct {
+  void *items[BRANCH_FACTOR];
+  unsigned int refCount;
+} VNode;
+
+#define NODE_CACHE_MAX_SIZE 1024
+
+typedef struct {
+  unsigned int size;
+  VNode* nodes[NODE_CACHE_MAX_SIZE];
+} vNodeCache;
+
+static vNodeCache nodeCache;
+
+typedef struct {
+  PyObject_HEAD
+  unsigned int count;   // Perhaps ditch this one in favor of ob_size/Py_SIZE()
+  unsigned int shift;
+  VNode *root;
+  VNode *tail;
+  PyObject *in_weakreflist; /* List of weak references */
+} PVector;
+
+typedef struct {
+  PyObject_HEAD
+  PVector* originalVector;
+  PVector* newVector;
+  PyObject* appendList;
+} PVectorEvolver;
+
+
+static PVector* EMPTY_VECTOR = NULL;
+static PyObject* transform_fn = NULL;
+
+static PyObject* transform(PVector* self, PyObject* args) {
+  if(transform_fn == NULL) {
+    // transform to avoid circular import problems
+    transform_fn = PyObject_GetAttrString(PyImport_ImportModule("pyrsistent._transformations"), "transform");
+  }
+
+  return PyObject_CallFunctionObjArgs(transform_fn, self, args, NULL);
+}
+
+
+// No access to internal members
+static PyMemberDef PVector_members[] = {
+	{NULL}  /* Sentinel */
+};
+
+#define debug(...)
+// #define debug printf
+
+#define NODE_REF_COUNT(n) ((n)->refCount)
+#define SET_NODE_REF_COUNT(n, c) (NODE_REF_COUNT(n) = (c))
+#define INC_NODE_REF_COUNT(n) (NODE_REF_COUNT(n)++)
+#define DEC_NODE_REF_COUNT(n) (NODE_REF_COUNT(n)--)
+
+static VNode* allocNode(void) {
+  if(nodeCache.size > 0) {
+    nodeCache.size--;
+    return nodeCache.nodes[nodeCache.size];
+  }
+
+  return PyMem_Malloc(sizeof(VNode));
+}
+
+static void freeNode(VNode *node) {
+  if(nodeCache.size < NODE_CACHE_MAX_SIZE) {
+    nodeCache.nodes[nodeCache.size] = node;
+    nodeCache.size++;
+  } else {
+    PyMem_Free(node);
+  }
+}
+
+static VNode* newNode(void) {
+  VNode* result = allocNode();
+  memset(result, 0x0, sizeof(VNode));
+  SET_NODE_REF_COUNT(result, 1);
+  debug("newNode() %p\n", result);
+  return result;
+}
+
+static VNode* copyNode(VNode* source) {
+  /* NB: Only to be used for internal nodes, eg. nodes that do not
+         hold direct references to python objects but only to other nodes. */
+  int i;
+  VNode* result = allocNode();
+  debug("copyNode() %p\n", result);
+  memcpy(result->items, source->items, sizeof(source->items));
+  
+  for(i = 0; i < BRANCH_FACTOR; i++) {
+    // TODO-OPT: Any need to go on when the first NULL has been found?
+    if(result->items[i] != NULL) {
+      INC_NODE_REF_COUNT((VNode*)result->items[i]);
+    }
+  }
+
+  SET_NODE_REF_COUNT(result, 1);
+  return result;
+}
+
+static PVector* emptyNewPvec(void);
+static PVector* copyPVector(PVector *original);
+static void extendWithItem(PVector *newVec, PyObject *item);
+
+static PyObject *PVectorEvolver_persistent(PVectorEvolver *);
+static int PVectorEvolver_set_item(PVectorEvolver *, PyObject*, PyObject*);
+
+static Py_ssize_t PVector_len(PVector *self) {
+  return self->count;
+}
+
+/* Convenience macros */
+#define ROOT_NODE_FULL(vec) ((vec->count >> SHIFT) > (1 << vec->shift))
+#define TAIL_OFF(vec) ((vec->count < BRANCH_FACTOR) ? 0 : (((vec->count - 1) >> SHIFT) << SHIFT))
+#define TAIL_SIZE(vec) (vec->count - TAIL_OFF(vec))
+#define PVector_CheckExact(op) (Py_TYPE(op) == &PVectorType)
+
+static VNode* nodeFor(PVector *self, int i){
+  int level;
+  if((i >= 0) && (i < self->count)) {
+    if(i >= TAIL_OFF(self)) {
+      return self->tail;
+    }
+
+    VNode* node = self->root;
+    for(level = self->shift; level > 0; level -= SHIFT) {
+      node = (VNode*) node->items[(i >> level) & BIT_MASK];
+    }
+
+    return node;
+  }
+
+  PyErr_Format(PyExc_IndexError, "Index out of range: %i", i);
+  return NULL;
+}
+
+static PyObject* _get_item(PVector *self, Py_ssize_t pos) {
+  VNode* node = nodeFor((PVector*)self, pos);
+  PyObject *result = NULL;
+  if(node != NULL) {
+    result = node->items[pos & BIT_MASK];
+  }
+  return result;
+}
+
+/*
+ Returns a new reference as specified by the PySequence_GetItem function.
+*/
+static PyObject* PVector_get_item(PVector *self, Py_ssize_t pos) {
+  if (pos < 0) {
+    pos += self->count;
+  }
+
+  PyObject* obj = _get_item(self, pos);
+  Py_XINCREF(obj);
+  return obj;  
+}
+
+static void releaseNode(int level, VNode *node) {
+  if(node == NULL) {
+    return;
+  }
+
+  debug("releaseNode(): node=%p, level=%i, refCount=%i\n", node, level, NODE_REF_COUNT(node));
+
+  int i;
+
+  DEC_NODE_REF_COUNT(node);
+  debug("Refcount when trying to release: %u\n", NODE_REF_COUNT(node));
+  if(NODE_REF_COUNT(node) == 0) {
+    if(level > 0) {
+      for(i = 0; i < BRANCH_FACTOR; i++) {
+        if(node->items[i] != NULL) {
+          releaseNode(level - SHIFT, node->items[i]);
+        }
+      }
+      freeNode(node);
+    } else {
+      for(i = 0; i < BRANCH_FACTOR; i++) {
+         Py_XDECREF(node->items[i]);
+      }
+      freeNode(node);
+    }
+  }
+
+  debug("releaseNode(): Done! node=%p!\n", node);
+}
+
+/*
+ Returns all references to PyObjects that have been stolen. Also decrements
+ the internal reference counts used for shared memory structures and deallocates
+ those if needed.
+*/
+static void PVector_dealloc(PVector *self) {
+  debug("Dealloc(): self=%p, self->count=%u, tail->refCount=%u, root->refCount=%u, self->shift=%u, self->tail=%p, self->root=%p\n",
+        self, self->count, NODE_REF_COUNT(self->tail), NODE_REF_COUNT(self->root), self->shift, self->tail, self->root);
+
+  if (self->in_weakreflist != NULL) {
+    PyObject_ClearWeakRefs((PyObject *) self);
+  }
+  
+  PyObject_GC_UnTrack((PyObject*)self);
+  Py_TRASHCAN_SAFE_BEGIN(self);
+
+  releaseNode(0, self->tail);
+  releaseNode(self->shift, self->root);
+  
+  PyObject_GC_Del(self);
+  Py_TRASHCAN_SAFE_END(self);
+}
+
+static PyObject *PVector_toList(PVector *self) {
+  Py_ssize_t i;
+  PyObject *list = PyList_New(self->count);
+  for (i = 0; i < self->count; ++i) {
+    PyObject *o = _get_item(self, i);
+    Py_INCREF(o);
+    PyList_SET_ITEM(list, i, o);
+  }
+
+  return list;
+}
+
+
+static PyObject *PVector_repr(PVector *self) {
+  // Reuse the list repr code, a bit less efficient but saves some code
+  PyObject *list = PVector_toList(self);
+  PyObject *list_repr = PyObject_Repr(list);
+  Py_DECREF(list);
+
+  if(list_repr == NULL) {
+    // Exception raised during call to repr
+    return NULL;
+  }
+  
+  // Repr for list implemented differently in python 2 and 3. Need to
+  // handle this or core dump will occur.
+#if PY_MAJOR_VERSION >= 3
+  PyObject *s = PyUnicode_FromFormat("%s%U%s", "pvector(", list_repr, ")");
+  Py_DECREF(list_repr);
+#else
+  PyObject *s = PyString_FromString("pvector(");
+  PyString_ConcatAndDel(&s, list_repr);
+  PyString_ConcatAndDel(&s, PyString_FromString(")"));
+#endif
+
+  return s;
+}
+
+
+static long PVector_hash(PVector *self) {
+  // Follows the pattern of the tuple hash
+  long x, y;
+  Py_ssize_t i;
+  long mult = 1000003L;
+  x = 0x456789L;
+  for(i=0; i<self->count; i++) {
+      y = PyObject_Hash(_get_item(self, i));
+      if (y == -1) {
+        return -1;
+      }
+      x = (x ^ y) * mult;
+      mult += (long)(82520L + i + i);
+  }
+
+  x += 97531L;
+  if(x == -1) {
+    x = -2;
+  }
+
+  return x;
+}
+
+static PyObject* compareSizes(long vlen, long wlen, int op) {
+    int cmp;
+    PyObject *res;
+    switch (op) {
+      case Py_LT: cmp = vlen <  wlen; break;
+      case Py_LE: cmp = vlen <= wlen; break;
+      case Py_EQ: cmp = vlen == wlen; break;
+      case Py_NE: cmp = vlen != wlen; break;
+      case Py_GT: cmp = vlen >  wlen; break;
+      case Py_GE: cmp = vlen >= wlen; break;
+      default: return NULL; /* cannot happen */
+    }
+
+    if (cmp) {
+      res = Py_True;
+    } else {
+      res = Py_False;
+    }
+
+    Py_INCREF(res);
+    return res;
+}
+
+static PyObject* PVector_richcompare(PyObject *v, PyObject *w, int op) {
+    // Follows the principles of the tuple comparison
+    PVector *vt, *wt;
+    Py_ssize_t i;
+    Py_ssize_t vlen, wlen;
+    PyObject *list;
+    PyObject *result;
+
+    if(!PVector_CheckExact(v) || !PVector_CheckExact(w)) {
+      if(PVector_CheckExact(v)) {
+        list = PVector_toList((PVector*)v);
+        result = PyObject_RichCompare(list , w, op);
+        Py_DECREF(list);
+        return result; 
+      }
+
+      if(PVector_CheckExact(w)) {
+        list = PVector_toList((PVector*)w);
+        result = PyObject_RichCompare(v, list, op);
+        Py_DECREF(list);
+        return result; 
+      }
+
+      Py_INCREF(Py_NotImplemented);
+      return Py_NotImplemented;
+    }
+
+    if((op == Py_EQ) && (v == w)) {
+        Py_INCREF(Py_True);
+        return Py_True;
+    }
+
+    vt = (PVector *)v;
+    wt = (PVector *)w;
+
+    vlen = vt->count;
+    wlen = wt->count;
+
+    if (vlen != wlen) {
+        if (op == Py_EQ) {
+            Py_INCREF(Py_False);
+            return Py_False;
+        } else if (op == Py_NE) {
+            Py_INCREF(Py_True);
+            return Py_True;
+        }
+    }
+
+    /* Search for the first index where items are different. */
+    PyObject *left = NULL;
+    PyObject *right = NULL;
+    for (i = 0; i < vlen && i < wlen; i++) {
+        left = _get_item(vt, i);
+        right = _get_item(wt, i);
+        int k = PyObject_RichCompareBool(left, right, Py_EQ);
+        if (k < 0) {
+            return NULL;
+        }
+        if (!k) {
+           break;
+        }
+    }
+
+    if (i >= vlen || i >= wlen) {
+        /* No more items to compare -- compare sizes */
+        return compareSizes(vlen, wlen, op);
+    }
+
+    /* We have an item that differs -- shortcuts for EQ/NE */
+    if (op == Py_EQ) {
+        Py_INCREF(Py_False);
+        return Py_False;
+    } else if (op == Py_NE) {
+        Py_INCREF(Py_True);
+        return Py_True;
+    } else {
+      /* Compare the final item again using the proper operator */
+      return PyObject_RichCompare(left, right, op);
+    }
+}
+
+
+static PyObject* PVector_repeat(PVector *self, Py_ssize_t n) {
+  if (n < 0) {
+      n = 0;
+  }
+
+  if ((n == 0) || (self->count == 0)) {
+    Py_INCREF(EMPTY_VECTOR);
+    return (PyObject *)EMPTY_VECTOR;
+  } else if (n == 1) {
+    Py_INCREF(self);
+    return (PyObject *)self;
+  } else if ((self->count * n)/self->count != n) {
+    return PyErr_NoMemory();
+  } else {
+    int i, j;
+    PVector *newVec = copyPVector(self);
+    for(i=0; i<(n-1); i++) {
+      for(j=0; j<self->count; j++) {
+        extendWithItem(newVec, PVector_get_item(self, j));
+      }
+    }
+    return (PyObject*)newVec;
+  }
+}
+
+static int PVector_traverse(PVector *o, visitproc visit, void *arg) {
+    // Naive traverse
+    Py_ssize_t i;
+    for (i = o->count; --i >= 0; ) {
+      Py_VISIT(_get_item(o, i));
+    }
+
+    return 0;
+}
+
+
+static PyObject* PVector_index(PVector *self, PyObject *args) {
+  // A direct rip-off of the tuple version
+  Py_ssize_t i, start=0, stop=self->count;
+  PyObject *value;
+  
+  if (!PyArg_ParseTuple(args, "O|O&O&:index", &value,
+			_PyEval_SliceIndex, &start,
+			_PyEval_SliceIndex, &stop)) {
+    return NULL;
+  }
+  
+  if (start < 0) {
+    start += self->count;
+    if (start < 0) {
+      start = 0;
+    }
+  }
+  
+  if (stop < 0) {
+    stop += self->count;
+      if (stop < 0) {
+	stop = 0;
+      }
+  }
+  
+  for (i = start; i < stop && i < self->count; i++) {
+    int cmp = PyObject_RichCompareBool(_get_item(self, i), value, Py_EQ);
+    if (cmp > 0) {
+#if PY_MAJOR_VERSION >= 3
+      return PyLong_FromSsize_t(i);
+#else
+      return PyInt_FromSsize_t(i);
+#endif
+    } else if (cmp < 0) {
+      return NULL;
+    }
+  }
+
+  PyErr_SetString(PyExc_ValueError, "PVector.index(x): x not in vector");
+  return NULL;
+}
+
+static PyObject* PVector_count(PVector *self, PyObject *value) {
+  Py_ssize_t count = 0;
+  Py_ssize_t i;
+
+  for (i = 0; i < self->count; i++) {
+    int cmp = PyObject_RichCompareBool(_get_item(self, i), value, Py_EQ);
+    if (cmp > 0) {
+      count++;
+    } else if (cmp < 0) {
+      return NULL;
+    }
+  }
+
+#if PY_MAJOR_VERSION >= 3
+      return PyLong_FromSsize_t(count);
+#else
+      return PyInt_FromSsize_t(count);
+#endif
+}
+
+static PyObject* PVector_pickle_reduce(PVector *self) {
+
+  PyObject* module = PyImport_ImportModule("pvectorc");
+  PyObject* pvector_fn = PyObject_GetAttrString(module, "pvector");
+  Py_DECREF(module);
+
+  PyObject *list = PVector_toList(self);
+  PyObject *arg_tuple = PyTuple_New(1);
+  PyTuple_SET_ITEM(arg_tuple, 0, list);
+
+  PyObject *result_tuple = PyTuple_New(2);
+  PyTuple_SET_ITEM(result_tuple, 0, pvector_fn);
+  PyTuple_SET_ITEM(result_tuple, 1, arg_tuple);
+
+  return result_tuple;
+}
+
+static PVector* rawCopyPVector(PVector* vector) {
+  PVector* newVector = PyObject_GC_New(PVector, &PVectorType);
+  newVector->count = vector->count;
+  newVector->shift = vector->shift;
+  newVector->root = vector->root;
+  newVector->tail = vector->tail;
+  newVector->in_weakreflist = NULL;
+  PyObject_GC_Track((PyObject*)newVector);
+  return newVector;
+}
+
+static void initializeEvolver(PVectorEvolver* evolver, PVector* vector, PyObject* appendList) {
+  // Need to hold a reference to the underlying vector to manage
+  // the ref counting properly.
+  evolver->originalVector = vector;
+  evolver->newVector = vector;
+
+  if(appendList == NULL) {
+    evolver->appendList = PyList_New(0);
+  } else {
+    evolver->appendList = appendList;
+  }
+}
+
+static PyObject * PVector_evolver(PVector *self) {
+  PVectorEvolver *evolver = PyObject_GC_New(PVectorEvolver, &PVectorEvolverType);
+  if (evolver == NULL) {
+    return NULL;
+  }
+  initializeEvolver(evolver, self, NULL);
+  PyObject_GC_Track(evolver);
+  Py_INCREF(self);
+  return (PyObject *)evolver;
+}
+
+
+static void copyInsert(void** dest, void** src, Py_ssize_t pos, void *obj) {
+  memcpy(dest, src, BRANCH_FACTOR * sizeof(void*));
+  dest[pos] = obj;
+}
+
+static PyObject* PVector_append(PVector *self, PyObject *obj);
+
+static PyObject* PVector_transform(PVector *self, PyObject *obj);
+
+static PyObject* PVector_set(PVector *self, PyObject *obj);
+
+static PyObject* PVector_mset(PVector *self, PyObject *args);
+
+static PyObject* PVector_subscript(PVector* self, PyObject* item);
+
+static PyObject* PVector_extend(PVector *self, PyObject *args);
+
+static PyObject* PVector_delete(PVector *self, PyObject *args);
+
+static PyObject* PVector_remove(PVector *self, PyObject *args);
+
+static PySequenceMethods PVector_sequence_methods = {
+    (lenfunc)PVector_len,            /* sq_length */
+    (binaryfunc)PVector_extend,      /* sq_concat */
+    (ssizeargfunc)PVector_repeat,    /* sq_repeat */
+    (ssizeargfunc)PVector_get_item,  /* sq_item */
+    // TODO might want to move the slice function to here
+    NULL,                            /* sq_slice */
+    NULL,                            /* sq_ass_item */
+    NULL,                            /* sq_ass_slice */
+    NULL,                            /* sq_contains */
+    NULL,                            /* sq_inplace_concat */
+    NULL,                            /* sq_inplace_repeat */
+};
+
+static PyMappingMethods PVector_mapping_methods = {
+    (lenfunc)PVector_len,
+    (binaryfunc)PVector_subscript,
+    NULL
+};
+
+
+static PyMethodDef PVector_methods[] = {
+	{"append",      (PyCFunction)PVector_append, METH_O,       "Appends an element"},
+	{"set",         (PyCFunction)PVector_set, METH_VARARGS, "Inserts an element at the specified position"},
+	{"extend",      (PyCFunction)PVector_extend, METH_O|METH_COEXIST, "Extend"},
+        {"transform",   (PyCFunction)PVector_transform, METH_VARARGS, "Apply one or more transformations"},
+        {"index",       (PyCFunction)PVector_index, METH_VARARGS, "Return first index of value"},
+	{"count",       (PyCFunction)PVector_count, METH_O, "Return number of occurrences of value"},
+        {"__reduce__",  (PyCFunction)PVector_pickle_reduce, METH_NOARGS, "Pickle support method"},
+        {"evolver",     (PyCFunction)PVector_evolver, METH_NOARGS, "Return new evolver for pvector"},
+	{"mset",        (PyCFunction)PVector_mset, METH_VARARGS, "Inserts multiple elements at the specified positions"},
+        {"tolist",      (PyCFunction)PVector_toList, METH_NOARGS, "Convert to list"},
+        {"delete",      (PyCFunction)PVector_delete, METH_VARARGS, "Delete element(s) by index"},
+        {"remove",      (PyCFunction)PVector_remove, METH_VARARGS, "Remove element(s) by equality"},
+	{NULL}
+};
+
+static PyObject * PVectorIter_iter(PyObject *seq);
+
+static PyTypeObject PVectorType = {
+  PyVarObject_HEAD_INIT(NULL, 0)
+  "pvectorc.PVector",                         /* tp_name        */
+  sizeof(PVector),                            /* tp_basicsize   */
+  0,		                              /* tp_itemsize    */
+  (destructor)PVector_dealloc,                /* tp_dealloc     */
+  0,                                          /* tp_print       */
+  0,                                          /* tp_getattr     */
+  0,                                          /* tp_setattr     */
+  0,                                          /* tp_compare     */
+  (reprfunc)PVector_repr,                     /* tp_repr        */
+  0,                                          /* tp_as_number   */
+  &PVector_sequence_methods,                  /* tp_as_sequence */
+  &PVector_mapping_methods,                   /* tp_as_mapping  */
+  (hashfunc)PVector_hash,                     /* tp_hash        */
+  0,                                          /* tp_call        */
+  0,                                          /* tp_str         */
+  0,                                          /* tp_getattro    */
+  0,                                          /* tp_setattro    */
+  0,                                          /* tp_as_buffer   */
+  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags       */
+  "Persistent vector",   	              /* tp_doc         */
+  (traverseproc)PVector_traverse,             /* tp_traverse       */
+  0,                                          /* tp_clear          */
+  PVector_richcompare,                        /* tp_richcompare    */
+  offsetof(PVector, in_weakreflist),          /* tp_weaklistoffset */
+  PVectorIter_iter,                           /* tp_iter           */
+  0,                                          /* tp_iternext       */
+  PVector_methods,                            /* tp_methods        */
+  PVector_members,                            /* tp_members        */
+  0,                                          /* tp_getset         */
+  0,                                          /* tp_base           */
+  0,                                          /* tp_dict           */
+  0,                                          /* tp_descr_get      */
+  0,                                          /* tp_descr_set      */
+  0,                                          /* tp_dictoffset     */
+};
+
+static PyObject* pyrsistent_pvec(PyObject *self, PyObject *args) {
+    debug("pyrsistent_pvec(): %x\n", args);
+
+    PyObject *argObj = NULL;  /* list of arguments */
+
+    if(!PyArg_ParseTuple(args, "|O", &argObj)) {
+      return NULL;
+    }
+
+    if(argObj == NULL) {
+      Py_INCREF(EMPTY_VECTOR);
+      return (PyObject*)EMPTY_VECTOR;
+    }
+
+    return PVector_extend(EMPTY_VECTOR, argObj);
+}
+
+static PVector* emptyNewPvec(void) {
+  PVector *pvec = PyObject_GC_New(PVector, &PVectorType);
+  debug("pymem alloc_new %x, ref cnt: %u\n", pvec, pvec->ob_refcnt);
+  pvec->count = (Py_ssize_t)0;
+  pvec->shift = SHIFT;
+  pvec->root = newNode();
+  pvec->tail = newNode();
+  pvec->in_weakreflist = NULL;
+  PyObject_GC_Track((PyObject*)pvec);
+  return pvec;
+}
+
+static void incRefs(PyObject **obj) {
+  // TODO-OPT: Would it be OK to exit on first NULL? Should not be any
+  //           non NULLs beyond a NULL.
+  int i;
+  for(i = 0; i < BRANCH_FACTOR; i++) {
+    Py_XINCREF(obj[i]);
+  }
+}
+
+
+static PVector* newPvec(unsigned int count, unsigned int shift, VNode *root) {
+  // TODO-OPT: Introduce object cache
+  PVector *pvec = PyObject_GC_New(PVector, &PVectorType);
+  debug("pymem alloc_copy %x, ref cnt: %u\n", pvec, pvec->ob_refcnt);
+  pvec->count = count;
+  pvec->shift = shift;
+  pvec->root = root;
+  pvec->tail = newNode();
+  pvec->in_weakreflist = NULL;
+  PyObject_GC_Track((PyObject*)pvec);
+  return pvec;
+}
+
+static VNode* newPath(unsigned int level, VNode* node){
+  if(level == 0) {
+    INC_NODE_REF_COUNT(node);
+    return node;
+  }
+  
+  VNode* result = newNode();
+  result->items[0] = newPath(level - SHIFT, node);
+  return result;
+}
+
+static VNode* pushTail(unsigned int level, unsigned int count, VNode* parent, VNode* tail) {
+  int subIndex = ((count - 1) >> level) & BIT_MASK;
+  VNode* result = copyNode(parent);
+  VNode* nodeToInsert;
+  VNode* child;
+  debug("pushTail(): count = %i, subIndex = %i\n", count, subIndex);
+
+  if(level == SHIFT) {
+    // We're at the bottom
+    INC_NODE_REF_COUNT(tail);
+    nodeToInsert = tail;
+  } else {
+    // More levels available in the tree
+    child = parent->items[subIndex];
+
+    if(child != NULL) {
+      nodeToInsert = pushTail(level - SHIFT, count, child, tail);
+
+      // Need to make an adjustment of the ref COUNT for the child node here since
+      // it was incremented in an earlier stage when the node was copied. Now the child
+      // node will be part of the path copy so the number of references to the original
+      // child will not increase at all.
+      DEC_NODE_REF_COUNT(child);
+    } else {
+      nodeToInsert = newPath(level - SHIFT, tail);
+    }
+  }
+  
+  result->items[subIndex] = nodeToInsert;
+  return result;
+}
+
+static PVector* copyPVector(PVector *original) {
+  PVector *newVec = newPvec(original->count, original->shift, original->root);
+  INC_NODE_REF_COUNT(original->root);
+  memcpy(newVec->tail->items, original->tail->items, TAIL_SIZE(original) * sizeof(void*));
+  incRefs((PyObject**)newVec->tail->items);
+  return newVec;
+}
+
+/* Does not steal a reference, this must be managed outside of this function */
+static void extendWithItem(PVector *newVec, PyObject *item) {
+  unsigned int tail_size = TAIL_SIZE(newVec);
+
+  if(tail_size >= BRANCH_FACTOR) {
+    VNode* new_root;
+    if(ROOT_NODE_FULL(newVec)) {
+      new_root = newNode();
+      new_root->items[0] = newVec->root;
+      new_root->items[1] = newPath(newVec->shift, newVec->tail);
+      newVec->shift += SHIFT;
+    } else {
+      new_root = pushTail(newVec->shift, newVec->count, newVec->root, newVec->tail);
+      releaseNode(newVec->shift, newVec->root);
+    }
+
+    newVec->root = new_root;
+
+    // Need to adjust the ref count of the old tail here since no new references were
+    // actually created, we just moved the tail.
+    DEC_NODE_REF_COUNT(newVec->tail);
+    newVec->tail = newNode();
+    tail_size = 0;
+  }
+
+  newVec->tail->items[tail_size] = item;    
+  newVec->count++;
+}
+
+
+#if PY_MAJOR_VERSION >= 3
+// This was changed in 3.2 but we do not claim compatibility with any older version of python 3.
+#define SLICE_CAST
+#else
+#define SLICE_CAST (PySliceObject *)
+#endif
+
+static PyObject *PVector_subscript(PVector* self, PyObject* item) {
+  if (PyIndex_Check(item)) {
+    Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+    if (i == -1 && PyErr_Occurred()) {
+      return NULL;
+    }
+    
+    return PVector_get_item(self, i);
+  } else if (PySlice_Check(item)) {
+    Py_ssize_t start, stop, step, slicelength, cur, i;
+    if (PySlice_GetIndicesEx(SLICE_CAST item, self->count,
+                             &start, &stop, &step, &slicelength) < 0) {
+      return NULL;
+    }
+    
+    debug("start=%i, stop=%i, step=%i\n", start, stop, step);
+    
+    if (slicelength <= 0) {
+      Py_INCREF(EMPTY_VECTOR);
+      return (PyObject*)EMPTY_VECTOR;
+    } else if((slicelength == self->count) && (step > 0)) {
+      Py_INCREF(self);
+      return (PyObject*)self;
+    } else {
+      PVector *newVec = copyPVector(EMPTY_VECTOR);
+      for (cur=start, i=0; i<slicelength; cur += (size_t)step, i++) {
+        extendWithItem(newVec, PVector_get_item(self, cur));
+      }
+      
+      return (PyObject*)newVec;
+    }
+  } else {
+    PyErr_Format(PyExc_TypeError, "pvector indices must be integers, not %.200s", Py_TYPE(item)->tp_name);
+    return NULL;
+  }
+} 
+
+/* A hack to get some of the error handling code away from the function
+   doing the actual work */
+#define HANDLE_ITERATION_ERROR()                         \
+    if (PyErr_Occurred()) {                              \
+      if (PyErr_ExceptionMatches(PyExc_StopIteration)) { \
+        PyErr_Clear();                                   \
+      } else {                                           \
+        return NULL;                                     \
+      }                                                  \
+    }
+
+
+/* Returns a new vector that is extended with the iterable b.
+   Takes a copy of the original vector and performs the extension in place on this
+   one for efficiency. 
+
+   These are some optimizations that could be done to this function,
+   these are not considered important enough yet though.
+   - Use the PySequence_Fast ops if the iterable is a list or a tuple (which it
+     whould probably often be)
+   - Only copy the original tail if it is not full
+   - No need to try to increment ref count in tail for the whole tail
+*/
+static PyObject* PVector_extend(PVector *self, PyObject *iterable) {
+    PyObject *it;
+    PyObject *(*iternext)(PyObject *);
+
+    it = PyObject_GetIter(iterable);
+    if (it == NULL) {
+        return NULL;
+    }
+    
+    // TODO-OPT: Use special fast iterator if available
+    iternext = *Py_TYPE(it)->tp_iternext;
+    PyObject *item = iternext(it);
+    if (item == NULL) {
+      Py_DECREF(it);
+      HANDLE_ITERATION_ERROR()
+      Py_INCREF(self);
+      return (PyObject *)self;
+    } else {
+      PVector *newVec = copyPVector(self);
+      // TODO-OPT test using special case code here for extension to
+      // avoid recalculating tail length all the time.
+      while(item != NULL) {
+        extendWithItem(newVec, item);
+        item = iternext(it);
+      }
+
+      Py_DECREF(it);
+      HANDLE_ITERATION_ERROR()
+      return (PyObject*)newVec;
+    }
+}
+
+/*
+ Steals a reference to the object that is appended to the list.
+*/
+static PyObject* PVector_append(PVector *self, PyObject *obj) {
+  assert (obj != NULL);
+
+  unsigned int tail_size = TAIL_SIZE(self);
+  debug("append(): count = %u, tail_size = %u\n", self->count, tail_size);
+
+  // Does the new object fit in the tail? If so, take a copy of the tail and
+  // insert the new element in that.
+  if(tail_size < BRANCH_FACTOR) {
+    INC_NODE_REF_COUNT(self->root);
+    PVector *new_pvec = newPvec(self->count + 1, self->shift, self->root);
+    // TODO-OPT No need to copy more than the current tail length
+    // TODO-OPT No need to incRefs for all elements all the time
+    copyInsert(new_pvec->tail->items, self->tail->items, tail_size, obj);
+    incRefs((PyObject**)new_pvec->tail->items);
+    debug("append(): new_pvec=%p, new_pvec->tail=%p, new_pvec->root=%p\n",
+    new_pvec, new_pvec->tail, new_pvec->root);
+
+    return (PyObject*)new_pvec;
+  }
+
+  // Tail is full, need to push it into the tree  
+  VNode* new_root;
+  unsigned int new_shift;
+  if(ROOT_NODE_FULL(self)) {
+    new_root = newNode();
+    new_root->items[0] = self->root;
+    INC_NODE_REF_COUNT(self->root);
+    new_root->items[1] = newPath(self->shift, self->tail);
+    new_shift = self->shift + SHIFT;
+  } else {
+    new_root = pushTail(self->shift, self->count, self->root, self->tail);
+    new_shift = self->shift;
+  }
+
+  PVector* pvec = newPvec(self->count + 1, new_shift, new_root);
+  pvec->tail->items[0] = obj;
+  Py_XINCREF(obj);
+  debug("append_push(): pvec=%p, pvec->tail=%p, pvec->root=%p\n", pvec, pvec->tail, pvec->root);
+  return (PyObject*)pvec;
+}
+
+static VNode* doSet(VNode* node, unsigned int level, unsigned int position, PyObject* value) {
+  debug("doSet(): level == %i\n", level);
+  if(level == 0) {
+    // TODO-OPT: Perhaps an alloc followed by a reset of reference
+    // count is enough here since we overwrite all subnodes below.
+    VNode* theNewNode = newNode();
+    copyInsert(theNewNode->items, node->items, position & BIT_MASK, value);
+    incRefs((PyObject**)theNewNode->items);
+    return theNewNode;
+  } else {
+    VNode* theNewNode = copyNode(node);
+    Py_ssize_t index = (position >> level) & BIT_MASK;
+
+    // Drop reference to this node since we're about to replace it
+    DEC_NODE_REF_COUNT((VNode*)theNewNode->items[index]);
+    theNewNode->items[index] = doSet(node->items[index], level - SHIFT, position, value); 
+    return theNewNode;
+  }
+}
+
+
+static PyObject* internalSet(PVector *self, Py_ssize_t position, PyObject *argObj) {
+  if(position < 0) {
+    position += self->count;
+  }
+
+  if((0 <= position) && (position < self->count)) {
+    if(position >= TAIL_OFF(self)) {
+      // Reuse the root, replace the tail
+      INC_NODE_REF_COUNT(self->root);
+      PVector *new_pvec = newPvec(self->count, self->shift, self->root);
+      copyInsert(new_pvec->tail->items, self->tail->items, position & BIT_MASK, argObj);
+      incRefs((PyObject**)new_pvec->tail->items);
+      return (PyObject*)new_pvec;
+    } else {
+      // Keep the tail, replace the root
+      VNode *newRoot = doSet(self->root, self->shift, position, argObj);
+      PVector *new_pvec = newPvec(self->count, self->shift, newRoot);
+
+      // Free the tail and replace it with a reference to the tail of the original vector
+      freeNode(new_pvec->tail);
+      new_pvec->tail = self->tail;
+      INC_NODE_REF_COUNT(self->tail);
+      return (PyObject*)new_pvec;
+    }
+  } else if (position == self->count) {
+    // TODO Remove this case?
+    return PVector_append(self, argObj);
+  } else {
+    PyErr_Format(PyExc_IndexError, "Index out of range: %zd", position);
+    return NULL;
+  }
+}
+
+static PyObject* PVector_transform(PVector *self, PyObject *obj) {
+  return transform(self, obj);
+}
+
+/*
+ Steals a reference to the object that is inserted in the vector.
+*/
+static PyObject* PVector_set(PVector *self, PyObject *args) {
+  PyObject *argObj = NULL;  /* argument to insert */
+  Py_ssize_t position;
+
+  /* The n parses for size, the O parses for a Python object */
+  if(!PyArg_ParseTuple(args, "nO", &position, &argObj)) {
+    return NULL;
+  }
+
+  return internalSet(self, position, argObj);
+}
+
+
+static PyObject* PVector_mset(PVector *self, PyObject *args) {
+  Py_ssize_t size = PyTuple_Size(args);
+  if(size % 2) {
+    PyErr_SetString(PyExc_TypeError, "mset expected an even number of arguments");
+    return NULL;
+  }
+
+  PVectorEvolver* evolver = (PVectorEvolver*)PVector_evolver(self);
+  Py_ssize_t i;
+  for(i=0; i<size; i+=2) {
+    if(PVectorEvolver_set_item(evolver, PyTuple_GetItem(args, i), PyTuple_GetItem(args, i + 1)) < 0) {
+      Py_DECREF(evolver);
+      return NULL;
+    }
+  }
+
+  PyObject* vector = PVectorEvolver_persistent(evolver);
+  Py_DECREF(evolver);
+  return vector;
+}
+
+
+static PyObject* internalDelete(PVector *self, Py_ssize_t index, PyObject *stop_obj) {
+  Py_ssize_t stop;
+  PyObject *list;
+  PyObject *result;
+
+  if (index < 0) {
+    index += self->count;
+  }
+
+  if (stop_obj != NULL) {
+    if (PyIndex_Check(stop_obj)) {
+      stop = PyNumber_AsSsize_t(stop_obj, PyExc_IndexError);
+      if (stop == -1 && PyErr_Occurred()) {
+        return NULL;
+      }
+    } else {
+      PyErr_Format(PyExc_TypeError, "Stop index must be integer, not %.200s", Py_TYPE(stop_obj)->tp_name);
+      return NULL;
+    }
+
+    if (stop < 0) {
+      stop += self->count;
+    }
+  } else {
+    if (index < 0 || index >= self->count) {
+      PyErr_SetString(PyExc_IndexError, "delete index out of range");
+      return NULL;
+    }
+
+    stop = index + 1;
+  }
+
+  list = PVector_toList(self);
+  if(PyList_SetSlice(list, index, stop, NULL) < 0) {
+    return NULL;
+  }
+
+  result = PVector_extend(EMPTY_VECTOR, list);
+  Py_DECREF(list);
+  return result;
+}
+
+static PyObject* PVector_delete(PVector *self, PyObject *args) {
+  Py_ssize_t index;
+  PyObject *stop_obj = NULL;
+
+  if(!PyArg_ParseTuple(args, "n|O:delete", &index, &stop_obj)) {
+    return NULL;
+  }
+
+  return internalDelete(self, index, stop_obj);
+}
+
+static PyObject* PVector_remove(PVector *self, PyObject *args) {
+  Py_ssize_t index;
+  PyObject* py_index = PVector_index(self, args);
+
+  if(py_index != NULL) {
+#if PY_MAJOR_VERSION >= 3
+      index = PyLong_AsSsize_t(py_index);
+#else
+      index = PyInt_AsSsize_t(py_index);
+#endif
+    Py_DECREF(py_index);
+    return internalDelete(self, index, NULL);
+  }
+
+  PyErr_SetString(PyExc_ValueError, "PVector.remove(x): x not in vector");
+  return NULL;
+}
+
+
+/*********************** PVector Iterator **************************/
+
+/* 
+The Sequence class provides us with a default iterator but the runtime
+overhead of using that compared to the iterator below is huge.
+*/
+
+typedef struct {
+    PyObject_HEAD
+    Py_ssize_t it_index;
+    PVector *it_seq; /* Set to NULL when iterator is exhausted */
+} PVectorIter;
+
+static void PVectorIter_dealloc(PVectorIter *);
+static int PVectorIter_traverse(PVectorIter *, visitproc, void *);
+static PyObject *PVectorIter_next(PVectorIter *);
+
+static PyMethodDef PVectorIter_methods[] = {
+    {NULL,              NULL}           /* sentinel */
+};
+
+static PyTypeObject PVectorIterType = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "pvector_iterator",                         /* tp_name */
+    sizeof(PVectorIter),                        /* tp_basicsize */
+    0,                                          /* tp_itemsize */
+    /* methods */
+    (destructor)PVectorIter_dealloc,            /* tp_dealloc */
+    0,                                          /* tp_print */
+    0,                                          /* tp_getattr */
+    0,                                          /* tp_setattr */
+    0,                                          /* tp_compare */
+    0,                                          /* tp_repr */
+    0,                                          /* tp_as_number */
+    0,                                          /* tp_as_sequence */
+    0,                                          /* tp_as_mapping */
+    0,                                          /* tp_hash */
+    0,                                          /* tp_call */
+    0,                                          /* tp_str */
+    PyObject_GenericGetAttr,                    /* tp_getattro */
+    0,                                          /* tp_setattro */
+    0,                                          /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
+    0,                                          /* tp_doc */
+    (traverseproc)PVectorIter_traverse,         /* tp_traverse */
+    0,                                          /* tp_clear */
+    0,                                          /* tp_richcompare */
+    0,                                          /* tp_weaklistoffset */
+    PyObject_SelfIter,                          /* tp_iter */
+    (iternextfunc)PVectorIter_next,             /* tp_iternext */
+    PVectorIter_methods,                        /* tp_methods */
+    0,                                          /* tp_members */
+};
+
+static PyObject *PVectorIter_iter(PyObject *seq) {
+    PVectorIter *it = PyObject_GC_New(PVectorIter, &PVectorIterType);
+    if (it == NULL) {
+        return NULL;
+    }
+
+    it->it_index = 0;
+    Py_INCREF(seq);
+    it->it_seq = (PVector *)seq;
+    PyObject_GC_Track(it);
+    return (PyObject *)it;
+}
+
+static void PVectorIter_dealloc(PVectorIter *it) {
+    PyObject_GC_UnTrack(it);
+    Py_XDECREF(it->it_seq);
+    PyObject_GC_Del(it);
+}
+
+static int PVectorIter_traverse(PVectorIter *it, visitproc visit, void *arg) {
+    Py_VISIT(it->it_seq);
+    return 0;
+}
+
+static PyObject *PVectorIter_next(PVectorIter *it) {
+    assert(it != NULL);
+    PVector *seq = it->it_seq;
+    if (seq == NULL) {
+        return NULL;
+    }
+
+    if (it->it_index < seq->count) {
+        PyObject *item = _get_item(seq, it->it_index);
+        ++it->it_index;
+        Py_INCREF(item);
+        return item;
+    }
+
+    Py_DECREF(seq);
+    it->it_seq = NULL;
+    return NULL;
+}
+
+
+/*********************** PVector Evolver **************************/
+
+/* 
+Evolver to make multi updates easier to work with and more efficient.
+*/
+
+static void PVectorEvolver_dealloc(PVectorEvolver *);
+static PyObject *PVectorEvolver_append(PVectorEvolver *, PyObject *);
+static PyObject *PVectorEvolver_extend(PVectorEvolver *, PyObject *);
+static PyObject *PVectorEvolver_set(PVectorEvolver *, PyObject *);
+static PyObject *PVectorEvolver_delete(PVectorEvolver *self, PyObject *args);
+static PyObject *PVectorEvolver_subscript(PVectorEvolver *, PyObject *);
+static PyObject *PVectorEvolver_persistent(PVectorEvolver *);
+static Py_ssize_t PVectorEvolver_len(PVectorEvolver *);
+static PyObject *PVectorEvolver_is_dirty(PVectorEvolver *);
+static int PVectorEvolver_traverse(PVectorEvolver *self, visitproc visit, void *arg);
+
+static PyMappingMethods PVectorEvolver_mapping_methods = {
+  (lenfunc)PVectorEvolver_len,
+  (binaryfunc)PVectorEvolver_subscript,
+  (objobjargproc)PVectorEvolver_set_item,
+};
+
+
+static PyMethodDef PVectorEvolver_methods[] = {
+	{"append",      (PyCFunction)PVectorEvolver_append, METH_O,       "Appends an element"},
+	{"extend",      (PyCFunction)PVectorEvolver_extend, METH_O|METH_COEXIST, "Extend"},
+	{"set",         (PyCFunction)PVectorEvolver_set, METH_VARARGS, "Set item"},
+        {"delete",      (PyCFunction)PVectorEvolver_delete, METH_VARARGS, "Delete item"},
+        {"persistent",  (PyCFunction)PVectorEvolver_persistent, METH_NOARGS, "Create PVector from evolver"},
+        {"is_dirty",    (PyCFunction)PVectorEvolver_is_dirty, METH_NOARGS, "Check if evolver contains modifications"},
+        {NULL,              NULL}           /* sentinel */
+};
+
+static PyTypeObject PVectorEvolverType = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "pvector_evolver",                          /* tp_name */
+    sizeof(PVectorEvolver),                     /* tp_basicsize */
+    0,                                          /* tp_itemsize */
+    /* methods */
+    (destructor)PVectorEvolver_dealloc,         /* tp_dealloc */
+    0,                                          /* tp_print */
+    0,                                          /* tp_getattr */
+    0,                                          /* tp_setattr */
+    0,                                          /* tp_compare */
+    0,                                          /* tp_repr */
+    0,                                          /* tp_as_number */
+    0,                                          /* tp_as_sequence */
+    &PVectorEvolver_mapping_methods,             /* tp_as_mapping */
+    0,                                          /* tp_hash */
+    0,                                          /* tp_call */
+    0,                                          /* tp_str */
+    PyObject_GenericGetAttr,                    /* tp_getattro */
+    0,                                          /* tp_setattro */
+    0,                                          /* tp_as_buffer */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
+    0,                                          /* tp_doc */
+    (traverseproc)PVectorEvolver_traverse,      /* tp_traverse       */
+    0,                                          /* tp_clear */
+    0,                                          /* tp_richcompare */
+    0,                                          /* tp_weaklistoffset */
+    0,                                          /* tp_iter */
+    0,                                          /* tp_iternext */
+    PVectorEvolver_methods,                     /* tp_methods */
+    0,                                          /* tp_members */
+};
+
+
+// Indicate that a node is "dirty" (has been updated by the evolver)
+// by setting the MSB of the refCount. This will be cleared when
+// creating a pvector from the evolver (cleaning it).
+#define DIRTY_BIT 0x80000000
+#define REF_COUNT_MASK (~DIRTY_BIT)
+#define IS_DIRTY(node) ((node)->refCount & DIRTY_BIT)
+#define SET_DIRTY(node) ((node)->refCount |= DIRTY_BIT)
+#define CLEAR_DIRTY(node) ((node)->refCount &= REF_COUNT_MASK)
+
+
+static void cleanNodeRecursively(VNode *node, int level) {
+  debug("Cleaning recursively node=%p, level=%u\n", node, level);
+
+  int i;
+  CLEAR_DIRTY(node);
+  SET_NODE_REF_COUNT(node, 1);
+  if(level > 0) {
+    for(i = 0; i < BRANCH_FACTOR; i++) {
+      VNode *nextNode = (VNode*)node->items[i];
+      if((nextNode != NULL) && IS_DIRTY(nextNode)) {
+        cleanNodeRecursively(nextNode, level - SHIFT);
+      }
+    }
+  }
+}
+
+static void cleanVector(PVector *vector) {
+  // Cleaning the vector means that all dirty indications are cleared
+  // and that the nodes that were dirty get a ref count of 1 since
+  // they are brand new. Once cleaned the vector can be released into
+  // the wild.
+  if(IS_DIRTY(vector->tail)) {
+    cleanNodeRecursively(vector->tail, 0);
+  } else {
+    INC_NODE_REF_COUNT(vector->tail);
+  }
+
+  if(IS_DIRTY(vector->root)) {
+    cleanNodeRecursively(vector->root, vector->shift);
+  } else {
+    INC_NODE_REF_COUNT(vector->root);
+  }
+}
+
+static void PVectorEvolver_dealloc(PVectorEvolver *self) {
+  PyObject_GC_UnTrack(self);
+  Py_TRASHCAN_SAFE_BEGIN(self);
+
+  if(self->originalVector != self->newVector) {
+    cleanVector(self->newVector);
+    Py_DECREF(self->newVector);
+  }
+
+  Py_DECREF(self->originalVector);
+  Py_DECREF(self->appendList);
+
+  PyObject_GC_Del(self);
+  Py_TRASHCAN_SAFE_END(self);
+}
+
+static PyObject *PVectorEvolver_append(PVectorEvolver *self, PyObject *args) {
+  if (PyList_Append(self->appendList, args) == 0) {
+    Py_INCREF(self);
+    return (PyObject*)self;
+  }
+
+  return NULL;
+}
+
+static PyObject *PVectorEvolver_extend(PVectorEvolver *self, PyObject *args) {
+  PyObject *retVal = _PyList_Extend((PyListObject *)self->appendList, args);
+  if (retVal == NULL) {
+    return NULL;
+  }
+
+  Py_DECREF(retVal);
+  Py_INCREF(self);
+  return (PyObject*)self;
+}
+
+static PyObject *PVectorEvolver_subscript(PVectorEvolver *self, PyObject *item) {
+  if (PyIndex_Check(item)) {
+    Py_ssize_t position = PyNumber_AsSsize_t(item, PyExc_IndexError);
+    if (position == -1 && PyErr_Occurred()) {
+      return NULL;
+    }
+
+    if (position < 0) {
+      position += self->newVector->count + PyList_GET_SIZE(self->appendList);
+    }
+
+    if(0 <= position && position < self->newVector->count) {
+      PyObject *result = _get_item(self->newVector, position);
+      Py_XINCREF(result);
+      return result;
+    } else if (0 <= position && position < (self->newVector->count + PyList_GET_SIZE(self->appendList))) {
+      PyObject *result = PyList_GetItem(self->appendList, position - self->newVector->count);
+      Py_INCREF(result);
+      return result;
+    } else {
+      PyErr_SetString(PyExc_IndexError, "Index out of range");
+    }
+  } else {
+    PyErr_Format(PyExc_TypeError, "Indices must be integers, not %.200s", item->ob_type->tp_name);
+  }
+
+  return NULL;
+}
+
+static VNode* doSetWithDirty(VNode* node, unsigned int level, unsigned int position, PyObject* value) {
+  VNode* resultNode;
+  debug("doSetWithDirty(): level == %i\n", level);
+  if(level == 0) {
+    if(!IS_DIRTY(node)) {
+      resultNode = allocNode();
+      copyInsert(resultNode->items, node->items, position & BIT_MASK, value);
+      incRefs((PyObject**)resultNode->items);
+      SET_DIRTY(resultNode);
+    } else {
+      resultNode = node;
+      Py_INCREF(value);
+      Py_DECREF(resultNode->items[position & BIT_MASK]);
+      resultNode->items[position & BIT_MASK] = value;
+    }
+  } else {
+    if(!IS_DIRTY(node)) {
+      resultNode = copyNode(node);
+      SET_DIRTY(resultNode);
+    } else {
+      resultNode = node;
+    }    
+
+    Py_ssize_t index = (position >> level) & BIT_MASK;
+    VNode* oldNode = (VNode*)resultNode->items[index];
+    resultNode->items[index] = doSetWithDirty(resultNode->items[index], level - SHIFT, position, value);
+
+    if(resultNode->items[index] != oldNode) {
+      // Node replaced, drop references to old node
+      DEC_NODE_REF_COUNT(oldNode);
+    }
+  }
+
+  return resultNode;
+}
+
+/*
+ Steals a reference to the object that is inserted in the vector.
+*/
+static PyObject *PVectorEvolver_set(PVectorEvolver *self, PyObject *args) {
+  PyObject *argObj = NULL;  /* argument to insert */
+  PyObject *position = NULL;
+
+  /* The n parses for size, the O parses for a Python object */
+  if(!PyArg_ParseTuple(args, "OO", &position, &argObj)) {
+    return NULL;
+  }
+
+  if(PVectorEvolver_set_item(self, position, argObj) < 0) {
+    return NULL;
+  }
+
+  Py_INCREF(self);
+  return (PyObject*)self;
+}
+
+static PyObject *PVectorEvolver_delete(PVectorEvolver *self, PyObject *args) {
+  PyObject *position = NULL;
+
+  /* The n parses for size, the O parses for a Python object */
+  if(!PyArg_ParseTuple(args, "O", &position)) {
+    return NULL;
+  }
+
+  if(PVectorEvolver_set_item(self, position, NULL) < 0) {
+    return NULL;
+  }
+
+  Py_INCREF(self);
+  return (PyObject*)self;
+}
+
+
+static int internalPVectorDelete(PVectorEvolver *self, Py_ssize_t position) {
+  // Delete element. Should be unusual. Simple but expensive operation
+  // that reuses the delete code for the vector. Realize the vector, delete on it and
+  // then reset the evolver to work on the new vector.
+  PVector *temp = (PVector*)PVectorEvolver_persistent(self);
+  PVector *temp2 = (PVector*)internalDelete(temp, position, NULL);
+  Py_DECREF(temp);
+
+  if(temp2 == NULL) {
+    return -1;
+  }
+
+  Py_DECREF(self->originalVector);
+  self->originalVector = temp2;
+  self->newVector = self->originalVector;
+  return 0;
+}
+
+static int PVectorEvolver_set_item(PVectorEvolver *self, PyObject* item, PyObject* value) {
+  if (PyIndex_Check(item)) {
+    Py_ssize_t position = PyNumber_AsSsize_t(item, PyExc_IndexError);
+    if (position == -1 && PyErr_Occurred()) {
+      return -1;
+    }
+         
+    if (position < 0) {
+      position += self->newVector->count + PyList_GET_SIZE(self->appendList);
+    }
+
+    if((0 <= position) && (position < self->newVector->count)) {
+      if(self->originalVector == self->newVector) {
+        // Create new vector since we're about to modify the original
+        self->newVector = rawCopyPVector(self->originalVector);
+      }
+
+      if(value != NULL) {
+        if(position < TAIL_OFF(self->newVector)) {
+          self->newVector->root = doSetWithDirty(self->newVector->root, self->newVector->shift, position, value);
+        } else {
+          self->newVector->tail = doSetWithDirty(self->newVector->tail, 0, position, value);
+        }
+
+        return 0;
+      }
+
+      return internalPVectorDelete(self, position);
+    } else if((0 <= position) && (position < (self->newVector->count + PyList_GET_SIZE(self->appendList)))) {
+      if (value != NULL) {
+        int result = PyList_SetItem(self->appendList, position - self->newVector->count, value); 
+        if(result == 0) {
+          Py_INCREF(value);
+        }
+        return result;
+      }
+
+      return internalPVectorDelete(self, position);
+    } else if((0 <= position)
+              && (position < (self->newVector->count + PyList_GET_SIZE(self->appendList) + 1))
+              && (value != NULL)) {
+        return PyList_Append(self->appendList, value);
+    } else {
+      PyErr_Format(PyExc_IndexError, "Index out of range: %zd", position);
+    }
+  } else {
+    PyErr_Format(PyExc_TypeError, "Indices must be integers, not %.200s", item->ob_type->tp_name);
+  }
+  return -1;
+}
+
+static PyObject *PVectorEvolver_persistent(PVectorEvolver *self) {
+  PVector *resultVector;
+  if(self->newVector != self->originalVector) {
+    cleanVector(self->newVector);
+    Py_DECREF(self->originalVector);
+  }
+
+  resultVector = self->newVector;
+
+  if(PyList_GET_SIZE(self->appendList)) {
+    PVector *oldVector = resultVector;
+    resultVector = (PVector*)PVector_extend(resultVector, self->appendList);
+    Py_DECREF(oldVector);
+    Py_DECREF(self->appendList);
+    self->appendList = NULL;
+  }
+
+  initializeEvolver(self, resultVector, self->appendList);
+  Py_INCREF(resultVector);  
+  return (PyObject*)resultVector;
+}
+
+static Py_ssize_t PVectorEvolver_len(PVectorEvolver *self) {
+  return self->newVector->count + PyList_GET_SIZE(self->appendList);
+}
+
+static PyObject* PVectorEvolver_is_dirty(PVectorEvolver *self) {
+  if((self->newVector != self->originalVector) || (PyList_GET_SIZE(self->appendList) > 0)) {
+    Py_INCREF(Py_True);
+    return Py_True;
+  }
+
+  Py_INCREF(Py_False);
+  return Py_False;
+}
+
+static int PVectorEvolver_traverse(PVectorEvolver *self, visitproc visit, void *arg) {
+  Py_VISIT(self->newVector);
+  if (self->newVector != self->originalVector) {
+      Py_VISIT(self->originalVector);
+  }
+  Py_VISIT(self->appendList);
+  return 0;
+}
+
+static PyMethodDef PyrsistentMethods[] = {
+  {"pvector", pyrsistent_pvec, METH_VARARGS, 
+   "pvector([iterable])\n"
+   "Create a new persistent vector containing the elements in iterable.\n\n"
+   ">>> v1 = pvector([1, 2, 3])\n"
+   ">>> v1\n"
+   "pvector([1, 2, 3])"},
+  {NULL, NULL, 0, NULL}
+};
+
+
+/********************* Python module initialization ************************/
+
+#if PY_MAJOR_VERSION >= 3
+  static struct PyModuleDef moduledef = {
+    PyModuleDef_HEAD_INIT,
+    "pvectorc",          /* m_name */
+    "Persistent vector", /* m_doc */
+    -1,                  /* m_size */
+    PyrsistentMethods,   /* m_methods */
+    NULL,                /* m_reload */
+    NULL,                /* m_traverse */
+    NULL,                /* m_clear */
+    NULL,                /* m_free */
+  };
+#endif
+
+static PyObject* pyrsistent_pvectorc_moduleinit(void) {
+  PyObject* m;
+  
+  // Only allow creation/initialization through factory method pvec
+  PVectorType.tp_init = NULL;
+  PVectorType.tp_new = NULL;
+
+  if (PyType_Ready(&PVectorType) < 0) {
+    return NULL;
+  }
+  if (PyType_Ready(&PVectorIterType) < 0) {
+    return NULL;
+  }
+  if (PyType_Ready(&PVectorEvolverType) < 0) {
+    return NULL;
+  }
+
+
+#if PY_MAJOR_VERSION >= 3
+  m = PyModule_Create(&moduledef);
+#else
+  m = Py_InitModule3("pvectorc", PyrsistentMethods, "Persistent vector");  
+#endif
+
+  if (m == NULL) {
+    return NULL;
+  }
+
+  if(EMPTY_VECTOR == NULL) {
+    EMPTY_VECTOR = emptyNewPvec();
+  }
+
+  nodeCache.size = 0;
+
+  Py_INCREF(&PVectorType);
+  PyModule_AddObject(m, "PVector", (PyObject *)&PVectorType);
+
+  return m;
+}
+
+#if PY_MAJOR_VERSION >= 3
+PyMODINIT_FUNC PyInit_pvectorc(void) {
+  return pyrsistent_pvectorc_moduleinit();
+}
+#else
+PyMODINIT_FUNC initpvectorc(void) {
+  pyrsistent_pvectorc_moduleinit();
+}
+#endif
diff --git a/third_party/python/pyrsistent/pyrsistent/__init__.py b/third_party/python/pyrsistent/pyrsistent/__init__.py
new file mode 100644
index 0000000000..be299658f3
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/__init__.py
@@ -0,0 +1,47 @@
+# -*- coding: utf-8 -*-
+
+from pyrsistent._pmap import pmap, m, PMap
+
+from pyrsistent._pvector import pvector, v, PVector
+
+from pyrsistent._pset import pset, s, PSet
+
+from pyrsistent._pbag import pbag, b, PBag
+
+from pyrsistent._plist import plist, l, PList
+
+from pyrsistent._pdeque import pdeque, dq, PDeque
+
+from pyrsistent._checked_types import (
+    CheckedPMap, CheckedPVector, CheckedPSet, InvariantException, CheckedKeyTypeError,
+    CheckedValueTypeError, CheckedType, optional)
+
+from pyrsistent._field_common import (
+    field, PTypeError, pset_field, pmap_field, pvector_field)
+
+from pyrsistent._precord import PRecord
+
+from pyrsistent._pclass import PClass, PClassMeta
+
+from pyrsistent._immutable import immutable
+
+from pyrsistent._helpers import freeze, thaw, mutant
+
+from pyrsistent._transformations import inc, discard, rex, ny
+
+from pyrsistent._toolz import get_in
+
+
+__all__ = ('pmap', 'm', 'PMap',
+           'pvector', 'v', 'PVector',
+           'pset', 's', 'PSet',
+           'pbag', 'b', 'PBag',
+           'plist', 'l', 'PList',
+           'pdeque', 'dq', 'PDeque',
+           'CheckedPMap', 'CheckedPVector', 'CheckedPSet', 'InvariantException', 'CheckedKeyTypeError', 'CheckedValueTypeError', 'CheckedType', 'optional',
+           'PRecord', 'field', 'pset_field', 'pmap_field', 'pvector_field',
+           'PClass', 'PClassMeta',
+           'immutable',
+           'freeze', 'thaw', 'mutant',
+           'get_in',
+           'inc', 'discard', 'rex', 'ny')
diff --git a/third_party/python/pyrsistent/pyrsistent/__init__.pyi b/third_party/python/pyrsistent/pyrsistent/__init__.pyi
new file mode 100644
index 0000000000..5909f7991a
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/__init__.pyi
@@ -0,0 +1,213 @@
+# flake8: noqa: E704
+# from https://gist.github.com/WuTheFWasThat/091a17d4b5cab597dfd5d4c2d96faf09
+# Stubs for pyrsistent (Python 3.6)
+
+from typing import Any
+from typing import AnyStr
+from typing import Callable
+from typing import Iterable
+from typing import Iterator
+from typing import List
+from typing import Optional
+from typing import Mapping
+from typing import MutableMapping
+from typing import Sequence
+from typing import Set
+from typing import Union
+from typing import Tuple
+from typing import Type
+from typing import TypeVar
+from typing import overload
+
+# see commit 08519aa for explanation of the re-export
+from pyrsistent.typing import CheckedKeyTypeError as CheckedKeyTypeError
+from pyrsistent.typing import CheckedPMap as CheckedPMap
+from pyrsistent.typing import CheckedPSet as CheckedPSet
+from pyrsistent.typing import CheckedPVector as CheckedPVector
+from pyrsistent.typing import CheckedType as CheckedType
+from pyrsistent.typing import CheckedValueTypeError as CheckedValueTypeError
+from pyrsistent.typing import InvariantException as InvariantException
+from pyrsistent.typing import PClass as PClass
+from pyrsistent.typing import PBag as PBag
+from pyrsistent.typing import PDeque as PDeque
+from pyrsistent.typing import PList as PList
+from pyrsistent.typing import PMap as PMap
+from pyrsistent.typing import PMapEvolver as PMapEvolver
+from pyrsistent.typing import PSet as PSet
+from pyrsistent.typing import PSetEvolver as PSetEvolver
+from pyrsistent.typing import PTypeError as PTypeError
+from pyrsistent.typing import PVector as PVector
+from pyrsistent.typing import PVectorEvolver as PVectorEvolver
+
+T = TypeVar('T')
+KT = TypeVar('KT')
+VT = TypeVar('VT')
+
+def pmap(initial: Union[Mapping[KT, VT], Iterable[Tuple[KT, VT]]] = {}, pre_size: int = 0) -> PMap[KT, VT]: ...
+def m(**kwargs: VT) -> PMap[str, VT]: ...
+
+def pvector(iterable: Iterable[T] = ...) -> PVector[T]: ...
+def v(*iterable: T) -> PVector[T]: ...
+
+def pset(iterable: Iterable[T] = (), pre_size: int = 8) -> PSet[T]: ...
+def s(*iterable: T) -> PSet[T]: ...
+
+# see class_test.py for use cases
+Invariant = Tuple[bool, Optional[Union[str, Callable[[], str]]]]
+
+@overload
+def field(
+    type: Union[Type[T], Sequence[Type[T]]] = ...,
+    invariant: Callable[[Any], Union[Invariant, Iterable[Invariant]]] = lambda _: (True, None),
+    initial: Any = object(),
+    mandatory: bool = False,
+    factory: Callable[[Any], T] = lambda x: x,
+    serializer: Callable[[Any, T], Any] = lambda _, value: value,
+) -> T: ...
+# The actual return value (_PField) is irrelevant after a PRecord has been instantiated,
+# see https://github.com/tobgu/pyrsistent/blob/master/pyrsistent/_precord.py#L10
+@overload
+def field(
+    type: Any = ...,
+    invariant: Callable[[Any], Union[Invariant, Iterable[Invariant]]] = lambda _: (True, None),
+    initial: Any = object(),
+    mandatory: bool = False,
+    factory: Callable[[Any], Any] = lambda x: x,
+    serializer: Callable[[Any, Any], Any] = lambda _, value: value,
+) -> Any: ...
+
+# Use precise types for the simplest use cases, but fall back to Any for
+# everything else. See record_test.py for the wide range of possible types for
+# item_type
+@overload
+def pset_field(
+    item_type: Type[T],
+    optional: bool = False,
+    initial: Iterable[T] = ...,
+) -> PSet[T]: ...
+@overload
+def pset_field(
+    item_type: Any,
+    optional: bool = False,
+    initial: Any = (),
+) -> PSet[Any]: ...
+
+@overload
+def pmap_field(
+    key_type: Type[KT],
+    value_type: Type[VT],
+    optional: bool = False,
+    invariant: Callable[[Any], Tuple[bool, Optional[str]]] = lambda _: (True, None),
+) -> PMap[KT, VT]: ...
+@overload
+def pmap_field(
+    key_type: Any,
+    value_type: Any,
+    optional: bool = False,
+    invariant: Callable[[Any], Tuple[bool, Optional[str]]] = lambda _: (True, None),
+) -> PMap[Any, Any]: ...
+
+@overload
+def pvector_field(
+    item_type: Type[T],
+    optional: bool = False,
+    initial: Iterable[T] = ...,
+) -> PVector[T]: ...
+@overload
+def pvector_field(
+    item_type: Any,
+    optional: bool = False,
+    initial: Any = (),
+) -> PVector[Any]: ...
+
+def pbag(elements: Iterable[T]) -> PBag[T]: ...
+def b(*elements: T) -> PBag[T]: ...
+
+def plist(iterable: Iterable[T] = (), reverse: bool = False) -> PList[T]: ...
+def l(*elements: T) -> PList[T]: ...
+
+def pdeque(iterable: Optional[Iterable[T]] = None, maxlen: Optional[int] = None) -> PDeque[T]: ...
+def dq(*iterable: T) -> PDeque[T]: ...
+
+@overload
+def optional(type: T) -> Tuple[T, Type[None]]: ...
+@overload
+def optional(*typs: Any) -> Tuple[Any, ...]: ...
+
+T_PRecord = TypeVar('T_PRecord', bound='PRecord')
+class PRecord(PMap[AnyStr, Any]):
+    _precord_fields: Mapping
+    _precord_initial_values: Mapping
+
+    def __hash__(self) -> int: ...
+    def __init__(self, **kwargs: Any) -> None: ...
+    def __iter__(self) -> Iterator[Any]: ...
+    def __len__(self) -> int: ...
+    @classmethod
+    def create(
+        cls: Type[T_PRecord],
+        kwargs: Mapping,
+        _factory_fields: Optional[Iterable] = None,
+        ignore_extra: bool = False,
+    ) -> T_PRecord: ...
+    # This is OK because T_PRecord is a concrete type
+    def discard(self: T_PRecord, key: KT) -> T_PRecord: ...
+    def remove(self: T_PRecord, key: KT) -> T_PRecord: ...
+
+    def serialize(self, format: Optional[Any] = ...) -> MutableMapping: ...
+
+    # From pyrsistent documentation:
+    #   This set function differs slightly from that in the PMap
+    #   class. First of all it accepts key-value pairs. Second it accepts multiple key-value
+    #   pairs to perform one, atomic, update of multiple fields.
+    @overload
+    def set(self, key: KT, val: VT) -> Any: ...
+    @overload
+    def set(self, **kwargs: VT) -> Any: ...
+
+def immutable(
+    members: Union[str, Iterable[str]] = '',
+    name: str = 'Immutable',
+    verbose: bool = False,
+) -> Tuple: ...  # actually a namedtuple
+
+# ignore mypy warning "Overloaded function signatures 1 and 5 overlap with
+# incompatible return types"
+@overload
+def freeze(o: Mapping[KT, VT]) -> PMap[KT, VT]: ... # type: ignore
+@overload
+def freeze(o: List[T]) -> PVector[T]: ... # type: ignore
+@overload
+def freeze(o: Tuple[T, ...]) -> Tuple[T, ...]: ...
+@overload
+def freeze(o: Set[T]) -> PSet[T]: ... # type: ignore
+@overload
+def freeze(o: T) -> T: ...
+
+
+@overload
+def thaw(o: PMap[KT, VT]) -> MutableMapping[KT, VT]: ... # type: ignore
+@overload
+def thaw(o: PVector[T]) -> List[T]: ... # type: ignore
+@overload
+def thaw(o: Tuple[T, ...]) -> Tuple[T, ...]: ...
+# collections.abc.MutableSet is kind of garbage:
+# https://stackoverflow.com/questions/24977898/why-does-collections-mutableset-not-bestow-an-update-method
+@overload
+def thaw(o: PSet[T]) -> Set[T]: ... # type: ignore
+@overload
+def thaw(o: T) -> T: ...
+
+def mutant(fn: Callable) -> Callable: ...
+
+def inc(x: int) -> int: ...
+@overload
+def discard(evolver: PMapEvolver[KT, VT], key: KT) -> None: ...
+@overload
+def discard(evolver: PVectorEvolver[T], key: int) -> None: ...
+@overload
+def discard(evolver: PSetEvolver[T], key: T) -> None: ...
+def rex(expr: str) -> Callable[[Any], bool]: ...
+def ny(_: Any) -> bool: ...
+
+def get_in(keys: Iterable, coll: Mapping, default: Optional[Any] = None, no_default: bool = False) -> Any: ...
diff --git a/third_party/python/pyrsistent/pyrsistent/_checked_types.py b/third_party/python/pyrsistent/pyrsistent/_checked_types.py
new file mode 100644
index 0000000000..293d989f13
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_checked_types.py
@@ -0,0 +1,542 @@
+from ._compat import Iterable
+import six
+
+from pyrsistent._compat import Enum, string_types
+from pyrsistent._pmap import PMap, pmap
+from pyrsistent._pset import PSet, pset
+from pyrsistent._pvector import PythonPVector, python_pvector
+
+
+class CheckedType(object):
+    """
+    Marker class to enable creation and serialization of checked object graphs.
+    """
+    __slots__ = ()
+
+    @classmethod
+    def create(cls, source_data, _factory_fields=None):
+        raise NotImplementedError()
+
+    def serialize(self, format=None):
+        raise NotImplementedError()
+
+
+def _restore_pickle(cls, data):
+    return cls.create(data, _factory_fields=set())
+
+
+class InvariantException(Exception):
+    """
+    Exception raised from a :py:class:`CheckedType` when invariant tests fail or when a mandatory
+    field is missing.
+
+    Contains two fields of interest:
+    invariant_errors, a tuple of error data for the failing invariants
+    missing_fields, a tuple of strings specifying the missing names
+    """
+
+    def __init__(self, error_codes=(), missing_fields=(), *args, **kwargs):
+        self.invariant_errors = tuple(e() if callable(e) else e for e in error_codes)
+        self.missing_fields = missing_fields
+        super(InvariantException, self).__init__(*args, **kwargs)
+
+    def __str__(self):
+        return super(InvariantException, self).__str__() + \
+            ", invariant_errors=[{invariant_errors}], missing_fields=[{missing_fields}]".format(
+            invariant_errors=', '.join(str(e) for e in self.invariant_errors),
+            missing_fields=', '.join(self.missing_fields))
+
+
+_preserved_iterable_types = (
+        Enum,
+)
+"""Some types are themselves iterable, but we want to use the type itself and
+not its members for the type specification. This defines a set of such types
+that we explicitly preserve.
+
+Note that strings are not such types because the string inputs we pass in are
+values, not types.
+"""
+
+
+def maybe_parse_user_type(t):
+    """Try to coerce a user-supplied type directive into a list of types.
+
+    This function should be used in all places where a user specifies a type,
+    for consistency.
+
+    The policy for what defines valid user input should be clear from the implementation.
+    """
+    is_type = isinstance(t, type)
+    is_preserved = isinstance(t, type) and issubclass(t, _preserved_iterable_types)
+    is_string = isinstance(t, string_types)
+    is_iterable = isinstance(t, Iterable)
+
+    if is_preserved:
+        return [t]
+    elif is_string:
+        return [t]
+    elif is_type and not is_iterable:
+        return [t]
+    elif is_iterable:
+        # Recur to validate contained types as well.
+        ts = t
+        return tuple(e for t in ts for e in maybe_parse_user_type(t))
+    else:
+        # If this raises because `t` cannot be formatted, so be it.
+        raise TypeError(
+            'Type specifications must be types or strings. Input: {}'.format(t)
+        )
+
+
+def maybe_parse_many_user_types(ts):
+    # Just a different name to communicate that you're parsing multiple user
+    # inputs. `maybe_parse_user_type` handles the iterable case anyway.
+    return maybe_parse_user_type(ts)
+
+
+def _store_types(dct, bases, destination_name, source_name):
+    maybe_types = maybe_parse_many_user_types([
+        d[source_name]
+        for d in ([dct] + [b.__dict__ for b in bases]) if source_name in d
+    ])
+
+    dct[destination_name] = maybe_types
+
+
+def _merge_invariant_results(result):
+    verdict = True
+    data = []
+    for verd, dat in result:
+        if not verd:
+            verdict = False
+            data.append(dat)
+
+    return verdict, tuple(data)
+
+
+def wrap_invariant(invariant):
+    # Invariant functions may return the outcome of several tests
+    # In those cases the results have to be merged before being passed
+    # back to the client.
+    def f(*args, **kwargs):
+        result = invariant(*args, **kwargs)
+        if isinstance(result[0], bool):
+            return result
+
+        return _merge_invariant_results(result)
+
+    return f
+
+
+def _all_dicts(bases, seen=None):
+    """
+    Yield each class in ``bases`` and each of their base classes.
+    """
+    if seen is None:
+        seen = set()
+    for cls in bases:
+        if cls in seen:
+            continue
+        seen.add(cls)
+        yield cls.__dict__
+        for b in _all_dicts(cls.__bases__, seen):
+            yield b
+
+
+def store_invariants(dct, bases, destination_name, source_name):
+    # Invariants are inherited
+    invariants = []
+    for ns in [dct] + list(_all_dicts(bases)):
+        try:
+            invariant = ns[source_name]
+        except KeyError:
+            continue
+        invariants.append(invariant)
+
+    if not all(callable(invariant) for invariant in invariants):
+        raise TypeError('Invariants must be callable')
+    dct[destination_name] = tuple(wrap_invariant(inv) for inv in invariants)
+
+
+class _CheckedTypeMeta(type):
+    def __new__(mcs, name, bases, dct):
+        _store_types(dct, bases, '_checked_types', '__type__')
+        store_invariants(dct, bases, '_checked_invariants', '__invariant__')
+
+        def default_serializer(self, _, value):
+            if isinstance(value, CheckedType):
+                return value.serialize()
+            return value
+
+        dct.setdefault('__serializer__', default_serializer)
+
+        dct['__slots__'] = ()
+
+        return super(_CheckedTypeMeta, mcs).__new__(mcs, name, bases, dct)
+
+
+class CheckedTypeError(TypeError):
+    def __init__(self, source_class, expected_types, actual_type, actual_value, *args, **kwargs):
+        super(CheckedTypeError, self).__init__(*args, **kwargs)
+        self.source_class = source_class
+        self.expected_types = expected_types
+        self.actual_type = actual_type
+        self.actual_value = actual_value
+
+
+class CheckedKeyTypeError(CheckedTypeError):
+    """
+    Raised when trying to set a value using a key with a type that doesn't match the declared type.
+
+    Attributes:
+    source_class -- The class of the collection
+    expected_types  -- Allowed types
+    actual_type -- The non matching type
+    actual_value -- Value of the variable with the non matching type
+    """
+    pass
+
+
+class CheckedValueTypeError(CheckedTypeError):
+    """
+    Raised when trying to set a value using a key with a type that doesn't match the declared type.
+
+    Attributes:
+    source_class -- The class of the collection
+    expected_types  -- Allowed types
+    actual_type -- The non matching type
+    actual_value -- Value of the variable with the non matching type
+    """
+    pass
+
+
+def _get_class(type_name):
+    module_name, class_name = type_name.rsplit('.', 1)
+    module = __import__(module_name, fromlist=[class_name])
+    return getattr(module, class_name)
+
+
+def get_type(typ):
+    if isinstance(typ, type):
+        return typ
+
+    return _get_class(typ)
+
+
+def get_types(typs):
+    return [get_type(typ) for typ in typs]
+
+
+def _check_types(it, expected_types, source_class, exception_type=CheckedValueTypeError):
+    if expected_types:
+        for e in it:
+            if not any(isinstance(e, get_type(t)) for t in expected_types):
+                actual_type = type(e)
+                msg = "Type {source_class} can only be used with {expected_types}, not {actual_type}".format(
+                    source_class=source_class.__name__,
+                    expected_types=tuple(get_type(et).__name__ for et in expected_types),
+                    actual_type=actual_type.__name__)
+                raise exception_type(source_class, expected_types, actual_type, e, msg)
+
+
+def _invariant_errors(elem, invariants):
+    return [data for valid, data in (invariant(elem) for invariant in invariants) if not valid]
+
+
+def _invariant_errors_iterable(it, invariants):
+    return sum([_invariant_errors(elem, invariants) for elem in it], [])
+
+
+def optional(*typs):
+    """ Convenience function to specify that a value may be of any of the types in type 'typs' or None """
+    return tuple(typs) + (type(None),)
+
+
+def _checked_type_create(cls, source_data, _factory_fields=None, ignore_extra=False):
+    if isinstance(source_data, cls):
+        return source_data
+
+    # Recursively apply create methods of checked types if the types of the supplied data
+    # does not match any of the valid types.
+    types = get_types(cls._checked_types)
+    checked_type = next((t for t in types if issubclass(t, CheckedType)), None)
+    if checked_type:
+        return cls([checked_type.create(data, ignore_extra=ignore_extra)
+                    if not any(isinstance(data, t) for t in types) else data
+                    for data in source_data])
+
+    return cls(source_data)
+
+@six.add_metaclass(_CheckedTypeMeta)
+class CheckedPVector(PythonPVector, CheckedType):
+    """
+    A CheckedPVector is a PVector which allows specifying type and invariant checks.
+
+    >>> class Positives(CheckedPVector):
+    ...     __type__ = (int, float)
+    ...     __invariant__ = lambda n: (n >= 0, 'Negative')
+    ...
+    >>> Positives([1, 2, 3])
+    Positives([1, 2, 3])
+    """
+
+    __slots__ = ()
+
+    def __new__(cls, initial=()):
+        if type(initial) == PythonPVector:
+            return super(CheckedPVector, cls).__new__(cls, initial._count, initial._shift, initial._root, initial._tail)
+
+        return CheckedPVector.Evolver(cls, python_pvector()).extend(initial).persistent()
+
+    def set(self, key, value):
+        return self.evolver().set(key, value).persistent()
+
+    def append(self, val):
+        return self.evolver().append(val).persistent()
+
+    def extend(self, it):
+        return self.evolver().extend(it).persistent()
+
+    create = classmethod(_checked_type_create)
+
+    def serialize(self, format=None):
+        serializer = self.__serializer__
+        return list(serializer(format, v) for v in self)
+
+    def __reduce__(self):
+        # Pickling support
+        return _restore_pickle, (self.__class__, list(self),)
+
+    class Evolver(PythonPVector.Evolver):
+        __slots__ = ('_destination_class', '_invariant_errors')
+
+        def __init__(self, destination_class, vector):
+            super(CheckedPVector.Evolver, self).__init__(vector)
+            self._destination_class = destination_class
+            self._invariant_errors = []
+
+        def _check(self, it):
+            _check_types(it, self._destination_class._checked_types, self._destination_class)
+            error_data = _invariant_errors_iterable(it, self._destination_class._checked_invariants)
+            self._invariant_errors.extend(error_data)
+
+        def __setitem__(self, key, value):
+            self._check([value])
+            return super(CheckedPVector.Evolver, self).__setitem__(key, value)
+
+        def append(self, elem):
+            self._check([elem])
+            return super(CheckedPVector.Evolver, self).append(elem)
+
+        def extend(self, it):
+            it = list(it)
+            self._check(it)
+            return super(CheckedPVector.Evolver, self).extend(it)
+
+        def persistent(self):
+            if self._invariant_errors:
+                raise InvariantException(error_codes=self._invariant_errors)
+
+            result = self._orig_pvector
+            if self.is_dirty() or (self._destination_class != type(self._orig_pvector)):
+                pv = super(CheckedPVector.Evolver, self).persistent().extend(self._extra_tail)
+                result = self._destination_class(pv)
+                self._reset(result)
+
+            return result
+
+    def __repr__(self):
+        return self.__class__.__name__ + "({0})".format(self.tolist())
+
+    __str__ = __repr__
+
+    def evolver(self):
+        return CheckedPVector.Evolver(self.__class__, self)
+
+
+@six.add_metaclass(_CheckedTypeMeta)
+class CheckedPSet(PSet, CheckedType):
+    """
+    A CheckedPSet is a PSet which allows specifying type and invariant checks.
+
+    >>> class Positives(CheckedPSet):
+    ...     __type__ = (int, float)
+    ...     __invariant__ = lambda n: (n >= 0, 'Negative')
+    ...
+    >>> Positives([1, 2, 3])
+    Positives([1, 2, 3])
+    """
+
+    __slots__ = ()
+
+    def __new__(cls, initial=()):
+        if type(initial) is PMap:
+            return super(CheckedPSet, cls).__new__(cls, initial)
+
+        evolver = CheckedPSet.Evolver(cls, pset())
+        for e in initial:
+            evolver.add(e)
+
+        return evolver.persistent()
+
+    def __repr__(self):
+        return self.__class__.__name__ + super(CheckedPSet, self).__repr__()[4:]
+
+    def __str__(self):
+        return self.__repr__()
+
+    def serialize(self, format=None):
+        serializer = self.__serializer__
+        return set(serializer(format, v) for v in self)
+
+    create = classmethod(_checked_type_create)
+
+    def __reduce__(self):
+        # Pickling support
+        return _restore_pickle, (self.__class__, list(self),)
+
+    def evolver(self):
+        return CheckedPSet.Evolver(self.__class__, self)
+
+    class Evolver(PSet._Evolver):
+        __slots__ = ('_destination_class', '_invariant_errors')
+
+        def __init__(self, destination_class, original_set):
+            super(CheckedPSet.Evolver, self).__init__(original_set)
+            self._destination_class = destination_class
+            self._invariant_errors = []
+
+        def _check(self, it):
+            _check_types(it, self._destination_class._checked_types, self._destination_class)
+            error_data = _invariant_errors_iterable(it, self._destination_class._checked_invariants)
+            self._invariant_errors.extend(error_data)
+
+        def add(self, element):
+            self._check([element])
+            self._pmap_evolver[element] = True
+            return self
+
+        def persistent(self):
+            if self._invariant_errors:
+                raise InvariantException(error_codes=self._invariant_errors)
+
+            if self.is_dirty() or self._destination_class != type(self._original_pset):
+                return self._destination_class(self._pmap_evolver.persistent())
+
+            return self._original_pset
+
+
+class _CheckedMapTypeMeta(type):
+    def __new__(mcs, name, bases, dct):
+        _store_types(dct, bases, '_checked_key_types', '__key_type__')
+        _store_types(dct, bases, '_checked_value_types', '__value_type__')
+        store_invariants(dct, bases, '_checked_invariants', '__invariant__')
+
+        def default_serializer(self, _, key, value):
+            sk = key
+            if isinstance(key, CheckedType):
+                sk = key.serialize()
+
+            sv = value
+            if isinstance(value, CheckedType):
+                sv = value.serialize()
+
+            return sk, sv
+
+        dct.setdefault('__serializer__', default_serializer)
+
+        dct['__slots__'] = ()
+
+        return super(_CheckedMapTypeMeta, mcs).__new__(mcs, name, bases, dct)
+
+# Marker object
+_UNDEFINED_CHECKED_PMAP_SIZE = object()
+
+
+@six.add_metaclass(_CheckedMapTypeMeta)
+class CheckedPMap(PMap, CheckedType):
+    """
+    A CheckedPMap is a PMap which allows specifying type and invariant checks.
+
+    >>> class IntToFloatMap(CheckedPMap):
+    ...     __key_type__ = int
+    ...     __value_type__ = float
+    ...     __invariant__ = lambda k, v: (int(v) == k, 'Invalid mapping')
+    ...
+    >>> IntToFloatMap({1: 1.5, 2: 2.25})
+    IntToFloatMap({1: 1.5, 2: 2.25})
+    """
+
+    __slots__ = ()
+
+    def __new__(cls, initial={}, size=_UNDEFINED_CHECKED_PMAP_SIZE):
+        if size is not _UNDEFINED_CHECKED_PMAP_SIZE:
+            return super(CheckedPMap, cls).__new__(cls, size, initial)
+
+        evolver = CheckedPMap.Evolver(cls, pmap())
+        for k, v in initial.items():
+            evolver.set(k, v)
+
+        return evolver.persistent()
+
+    def evolver(self):
+        return CheckedPMap.Evolver(self.__class__, self)
+
+    def __repr__(self):
+        return self.__class__.__name__ + "({0})".format(str(dict(self)))
+
+    __str__ = __repr__
+
+    def serialize(self, format=None):
+        serializer = self.__serializer__
+        return dict(serializer(format, k, v) for k, v in self.items())
+
+    @classmethod
+    def create(cls, source_data, _factory_fields=None):
+        if isinstance(source_data, cls):
+            return source_data
+
+        # Recursively apply create methods of checked types if the types of the supplied data
+        # does not match any of the valid types.
+        key_types = get_types(cls._checked_key_types)
+        checked_key_type = next((t for t in key_types if issubclass(t, CheckedType)), None)
+        value_types = get_types(cls._checked_value_types)
+        checked_value_type = next((t for t in value_types if issubclass(t, CheckedType)), None)
+
+        if checked_key_type or checked_value_type:
+            return cls(dict((checked_key_type.create(key) if checked_key_type and not any(isinstance(key, t) for t in key_types) else key,
+                             checked_value_type.create(value) if checked_value_type and not any(isinstance(value, t) for t in value_types) else value)
+                            for key, value in source_data.items()))
+
+        return cls(source_data)
+
+    def __reduce__(self):
+        # Pickling support
+        return _restore_pickle, (self.__class__, dict(self),)
+
+    class Evolver(PMap._Evolver):
+        __slots__ = ('_destination_class', '_invariant_errors')
+
+        def __init__(self, destination_class, original_map):
+            super(CheckedPMap.Evolver, self).__init__(original_map)
+            self._destination_class = destination_class
+            self._invariant_errors = []
+
+        def set(self, key, value):
+            _check_types([key], self._destination_class._checked_key_types, self._destination_class, CheckedKeyTypeError)
+            _check_types([value], self._destination_class._checked_value_types, self._destination_class)
+            self._invariant_errors.extend(data for valid, data in (invariant(key, value)
+                                                                   for invariant in self._destination_class._checked_invariants)
+                                          if not valid)
+
+            return super(CheckedPMap.Evolver, self).set(key, value)
+
+        def persistent(self):
+            if self._invariant_errors:
+                raise InvariantException(error_codes=self._invariant_errors)
+
+            if self.is_dirty() or type(self._original_pmap) != self._destination_class:
+                return self._destination_class(self._buckets_evolver.persistent(), self._size)
+
+            return self._original_pmap
diff --git a/third_party/python/pyrsistent/pyrsistent/_compat.py b/third_party/python/pyrsistent/pyrsistent/_compat.py
new file mode 100644
index 0000000000..e728586afe
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_compat.py
@@ -0,0 +1,31 @@
+from six import string_types
+
+
+# enum compat
+try:
+    from enum import Enum
+except:
+    class Enum(object): pass
+    # no objects will be instances of this class
+
+# collections compat
+try:
+    from collections.abc import (
+        Container,
+        Hashable,
+        Iterable,
+        Mapping,
+        Sequence,
+        Set,
+        Sized,
+    )
+except ImportError:
+    from collections import (
+        Container,
+        Hashable,
+        Iterable,
+        Mapping,
+        Sequence,
+        Set,
+        Sized,
+    )
diff --git a/third_party/python/pyrsistent/pyrsistent/_field_common.py b/third_party/python/pyrsistent/pyrsistent/_field_common.py
new file mode 100644
index 0000000000..ca1cccd43c
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_field_common.py
@@ -0,0 +1,330 @@
+import six
+import sys
+
+from pyrsistent._checked_types import (
+    CheckedPMap,
+    CheckedPSet,
+    CheckedPVector,
+    CheckedType,
+    InvariantException,
+    _restore_pickle,
+    get_type,
+    maybe_parse_user_type,
+    maybe_parse_many_user_types,
+)
+from pyrsistent._checked_types import optional as optional_type
+from pyrsistent._checked_types import wrap_invariant
+import inspect
+
+PY2 = sys.version_info[0] < 3
+
+
+def set_fields(dct, bases, name):
+    dct[name] = dict(sum([list(b.__dict__.get(name, {}).items()) for b in bases], []))
+
+    for k, v in list(dct.items()):
+        if isinstance(v, _PField):
+            dct[name][k] = v
+            del dct[k]
+
+
+def check_global_invariants(subject, invariants):
+    error_codes = tuple(error_code for is_ok, error_code in
+                        (invariant(subject) for invariant in invariants) if not is_ok)
+    if error_codes:
+        raise InvariantException(error_codes, (), 'Global invariant failed')
+
+
+def serialize(serializer, format, value):
+    if isinstance(value, CheckedType) and serializer is PFIELD_NO_SERIALIZER:
+        return value.serialize(format)
+
+    return serializer(format, value)
+
+
+def check_type(destination_cls, field, name, value):
+    if field.type and not any(isinstance(value, get_type(t)) for t in field.type):
+        actual_type = type(value)
+        message = "Invalid type for field {0}.{1}, was {2}".format(destination_cls.__name__, name, actual_type.__name__)
+        raise PTypeError(destination_cls, name, field.type, actual_type, message)
+
+
+def is_type_cls(type_cls, field_type):
+    if type(field_type) is set:
+        return True
+    types = tuple(field_type)
+    if len(types) == 0:
+        return False
+    return issubclass(get_type(types[0]), type_cls)
+
+
+def is_field_ignore_extra_complaint(type_cls, field, ignore_extra):
+    # ignore_extra param has default False value, for speed purpose no need to propagate False
+    if not ignore_extra:
+        return False
+
+    if not is_type_cls(type_cls, field.type):
+        return False
+
+    if PY2:
+        return 'ignore_extra' in inspect.getargspec(field.factory).args
+    else:
+        return 'ignore_extra' in inspect.signature(field.factory).parameters
+
+
+
+class _PField(object):
+    __slots__ = ('type', 'invariant', 'initial', 'mandatory', '_factory', 'serializer')
+
+    def __init__(self, type, invariant, initial, mandatory, factory, serializer):
+        self.type = type
+        self.invariant = invariant
+        self.initial = initial
+        self.mandatory = mandatory
+        self._factory = factory
+        self.serializer = serializer
+
+    @property
+    def factory(self):
+        # If no factory is specified and the type is another CheckedType use the factory method of that CheckedType
+        if self._factory is PFIELD_NO_FACTORY and len(self.type) == 1:
+            typ = get_type(tuple(self.type)[0])
+            if issubclass(typ, CheckedType):
+                return typ.create
+
+        return self._factory
+
+PFIELD_NO_TYPE = ()
+PFIELD_NO_INVARIANT = lambda _: (True, None)
+PFIELD_NO_FACTORY = lambda x: x
+PFIELD_NO_INITIAL = object()
+PFIELD_NO_SERIALIZER = lambda _, value: value
+
+
+def field(type=PFIELD_NO_TYPE, invariant=PFIELD_NO_INVARIANT, initial=PFIELD_NO_INITIAL,
+          mandatory=False, factory=PFIELD_NO_FACTORY, serializer=PFIELD_NO_SERIALIZER):
+    """
+    Field specification factory for :py:class:`PRecord`.
+
+    :param type: a type or iterable with types that are allowed for this field
+    :param invariant: a function specifying an invariant that must hold for the field
+    :param initial: value of field if not specified when instantiating the record
+    :param mandatory: boolean specifying if the field is mandatory or not
+    :param factory: function called when field is set.
+    :param serializer: function that returns a serialized version of the field
+    """
+
+    # NB: We have to check this predicate separately from the predicates in
+    # `maybe_parse_user_type` et al. because this one is related to supporting
+    # the argspec for `field`, while those are related to supporting the valid
+    # ways to specify types.
+
+    # Multiple types must be passed in one of the following containers. Note
+    # that a type that is a subclass of one of these containers, like a
+    # `collections.namedtuple`, will work as expected, since we check
+    # `isinstance` and not `issubclass`.
+    if isinstance(type, (list, set, tuple)):
+        types = set(maybe_parse_many_user_types(type))
+    else:
+        types = set(maybe_parse_user_type(type))
+
+    invariant_function = wrap_invariant(invariant) if invariant != PFIELD_NO_INVARIANT and callable(invariant) else invariant
+    field = _PField(type=types, invariant=invariant_function, initial=initial,
+                    mandatory=mandatory, factory=factory, serializer=serializer)
+
+    _check_field_parameters(field)
+
+    return field
+
+
+def _check_field_parameters(field):
+    for t in field.type:
+        if not isinstance(t, type) and not isinstance(t, six.string_types):
+            raise TypeError('Type parameter expected, not {0}'.format(type(t)))
+
+    if field.initial is not PFIELD_NO_INITIAL and \
+            not callable(field.initial) and \
+            field.type and not any(isinstance(field.initial, t) for t in field.type):
+        raise TypeError('Initial has invalid type {0}'.format(type(field.initial)))
+
+    if not callable(field.invariant):
+        raise TypeError('Invariant must be callable')
+
+    if not callable(field.factory):
+        raise TypeError('Factory must be callable')
+
+    if not callable(field.serializer):
+        raise TypeError('Serializer must be callable')
+
+
+class PTypeError(TypeError):
+    """
+    Raised when trying to assign a value with a type that doesn't match the declared type.
+
+    Attributes:
+    source_class -- The class of the record
+    field -- Field name
+    expected_types  -- Types allowed for the field
+    actual_type -- The non matching type
+    """
+    def __init__(self, source_class, field, expected_types, actual_type, *args, **kwargs):
+        super(PTypeError, self).__init__(*args, **kwargs)
+        self.source_class = source_class
+        self.field = field
+        self.expected_types = expected_types
+        self.actual_type = actual_type
+
+
+SEQ_FIELD_TYPE_SUFFIXES = {
+    CheckedPVector: "PVector",
+    CheckedPSet: "PSet",
+}
+
+# Global dictionary to hold auto-generated field types: used for unpickling
+_seq_field_types = {}
+
+def _restore_seq_field_pickle(checked_class, item_type, data):
+    """Unpickling function for auto-generated PVec/PSet field types."""
+    type_ = _seq_field_types[checked_class, item_type]
+    return _restore_pickle(type_, data)
+
+def _types_to_names(types):
+    """Convert a tuple of types to a human-readable string."""
+    return "".join(get_type(typ).__name__.capitalize() for typ in types)
+
+def _make_seq_field_type(checked_class, item_type):
+    """Create a subclass of the given checked class with the given item type."""
+    type_ = _seq_field_types.get((checked_class, item_type))
+    if type_ is not None:
+        return type_
+
+    class TheType(checked_class):
+        __type__ = item_type
+
+        def __reduce__(self):
+            return (_restore_seq_field_pickle,
+                    (checked_class, item_type, list(self)))
+
+    suffix = SEQ_FIELD_TYPE_SUFFIXES[checked_class]
+    TheType.__name__ = _types_to_names(TheType._checked_types) + suffix
+    _seq_field_types[checked_class, item_type] = TheType
+    return TheType
+
+def _sequence_field(checked_class, item_type, optional, initial):
+    """
+    Create checked field for either ``PSet`` or ``PVector``.
+
+    :param checked_class: ``CheckedPSet`` or ``CheckedPVector``.
+    :param item_type: The required type for the items in the set.
+    :param optional: If true, ``None`` can be used as a value for
+        this field.
+    :param initial: Initial value to pass to factory.
+
+    :return: A ``field`` containing a checked class.
+    """
+    TheType = _make_seq_field_type(checked_class, item_type)
+
+    if optional:
+        def factory(argument, _factory_fields=None, ignore_extra=False):
+            if argument is None:
+                return None
+            else:
+                return TheType.create(argument, _factory_fields=_factory_fields, ignore_extra=ignore_extra)
+    else:
+        factory = TheType.create
+
+    return field(type=optional_type(TheType) if optional else TheType,
+                 factory=factory, mandatory=True,
+                 initial=factory(initial))
+
+
+def pset_field(item_type, optional=False, initial=()):
+    """
+    Create checked ``PSet`` field.
+
+    :param item_type: The required type for the items in the set.
+    :param optional: If true, ``None`` can be used as a value for
+        this field.
+    :param initial: Initial value to pass to factory if no value is given
+        for the field.
+
+    :return: A ``field`` containing a ``CheckedPSet`` of the given type.
+    """
+    return _sequence_field(CheckedPSet, item_type, optional,
+                           initial)
+
+
+def pvector_field(item_type, optional=False, initial=()):
+    """
+    Create checked ``PVector`` field.
+
+    :param item_type: The required type for the items in the vector.
+    :param optional: If true, ``None`` can be used as a value for
+        this field.
+    :param initial: Initial value to pass to factory if no value is given
+        for the field.
+
+    :return: A ``field`` containing a ``CheckedPVector`` of the given type.
+    """
+    return _sequence_field(CheckedPVector, item_type, optional,
+                           initial)
+
+
+_valid = lambda item: (True, "")
+
+
+# Global dictionary to hold auto-generated field types: used for unpickling
+_pmap_field_types = {}
+
+def _restore_pmap_field_pickle(key_type, value_type, data):
+    """Unpickling function for auto-generated PMap field types."""
+    type_ = _pmap_field_types[key_type, value_type]
+    return _restore_pickle(type_, data)
+
+def _make_pmap_field_type(key_type, value_type):
+    """Create a subclass of CheckedPMap with the given key and value types."""
+    type_ = _pmap_field_types.get((key_type, value_type))
+    if type_ is not None:
+        return type_
+
+    class TheMap(CheckedPMap):
+        __key_type__ = key_type
+        __value_type__ = value_type
+
+        def __reduce__(self):
+            return (_restore_pmap_field_pickle,
+                    (self.__key_type__, self.__value_type__, dict(self)))
+
+    TheMap.__name__ = "{0}To{1}PMap".format(
+        _types_to_names(TheMap._checked_key_types),
+        _types_to_names(TheMap._checked_value_types))
+    _pmap_field_types[key_type, value_type] = TheMap
+    return TheMap
+
+
+def pmap_field(key_type, value_type, optional=False, invariant=PFIELD_NO_INVARIANT):
+    """
+    Create a checked ``PMap`` field.
+
+    :param key: The required type for the keys of the map.
+    :param value: The required type for the values of the map.
+    :param optional: If true, ``None`` can be used as a value for
+        this field.
+    :param invariant: Pass-through to ``field``.
+
+    :return: A ``field`` containing a ``CheckedPMap``.
+    """
+    TheMap = _make_pmap_field_type(key_type, value_type)
+
+    if optional:
+        def factory(argument):
+            if argument is None:
+                return None
+            else:
+                return TheMap.create(argument)
+    else:
+        factory = TheMap.create
+
+    return field(mandatory=True, initial=TheMap(),
+                 type=optional_type(TheMap) if optional else TheMap,
+                 factory=factory, invariant=invariant)
diff --git a/third_party/python/pyrsistent/pyrsistent/_helpers.py b/third_party/python/pyrsistent/pyrsistent/_helpers.py
new file mode 100644
index 0000000000..c9c58feac5
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_helpers.py
@@ -0,0 +1,82 @@
+from functools import wraps
+import six
+from pyrsistent._pmap import PMap, pmap
+from pyrsistent._pset import PSet, pset
+from pyrsistent._pvector import PVector, pvector
+
+
+def freeze(o):
+    """
+    Recursively convert simple Python containers into pyrsistent versions
+    of those containers.
+
+    - list is converted to pvector, recursively
+    - dict is converted to pmap, recursively on values (but not keys)
+    - set is converted to pset, but not recursively
+    - tuple is converted to tuple, recursively.
+
+    Sets and dict keys are not recursively frozen because they do not contain
+    mutable data by convention. The main exception to this rule is that
+    dict keys and set elements are often instances of mutable objects that
+    support hash-by-id, which this function can't convert anyway.
+
+    >>> freeze(set([1, 2]))
+    pset([1, 2])
+    >>> freeze([1, {'a': 3}])
+    pvector([1, pmap({'a': 3})])
+    >>> freeze((1, []))
+    (1, pvector([]))
+    """
+    typ = type(o)
+    if typ is dict:
+        return pmap(dict((k, freeze(v)) for k, v in six.iteritems(o)))
+    if typ is list:
+        return pvector(map(freeze, o))
+    if typ is tuple:
+        return tuple(map(freeze, o))
+    if typ is set:
+        return pset(o)
+    return o
+
+
+def thaw(o):
+    """
+    Recursively convert pyrsistent containers into simple Python containers.
+
+    - pvector is converted to list, recursively
+    - pmap is converted to dict, recursively on values (but not keys)
+    - pset is converted to set, but not recursively
+    - tuple is converted to tuple, recursively.
+
+    >>> from pyrsistent import s, m, v
+    >>> thaw(s(1, 2))
+    {1, 2}
+    >>> thaw(v(1, m(a=3)))
+    [1, {'a': 3}]
+    >>> thaw((1, v()))
+    (1, [])
+    """
+    if isinstance(o, PVector):
+        return list(map(thaw, o))
+    if isinstance(o, PMap):
+        return dict((k, thaw(v)) for k, v in o.iteritems())
+    if isinstance(o, PSet):
+        return set(o)
+    if type(o) is tuple:
+        return tuple(map(thaw, o))
+    return o
+
+
+def mutant(fn):
+    """
+    Convenience decorator to isolate mutation to within the decorated function (with respect
+    to the input arguments).
+
+    All arguments to the decorated function will be frozen so that they are guaranteed not to change.
+    The return value is also frozen.
+    """
+    @wraps(fn)
+    def inner_f(*args, **kwargs):
+        return freeze(fn(*[freeze(e) for e in args], **dict(freeze(item) for item in kwargs.items())))
+
+    return inner_f
diff --git a/third_party/python/pyrsistent/pyrsistent/_immutable.py b/third_party/python/pyrsistent/pyrsistent/_immutable.py
new file mode 100644
index 0000000000..a89bd7552f
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_immutable.py
@@ -0,0 +1,105 @@
+import sys
+
+import six
+
+
+def immutable(members='', name='Immutable', verbose=False):
+    """
+    Produces a class that either can be used standalone or as a base class for persistent classes.
+
+    This is a thin wrapper around a named tuple.
+
+    Constructing a type and using it to instantiate objects:
+
+    >>> Point = immutable('x, y', name='Point')
+    >>> p = Point(1, 2)
+    >>> p2 = p.set(x=3)
+    >>> p
+    Point(x=1, y=2)
+    >>> p2
+    Point(x=3, y=2)
+
+    Inheriting from a constructed type. In this case no type name needs to be supplied:
+
+    >>> class PositivePoint(immutable('x, y')):
+    ...     __slots__ = tuple()
+    ...     def __new__(cls, x, y):
+    ...         if x > 0 and y > 0:
+    ...             return super(PositivePoint, cls).__new__(cls, x, y)
+    ...         raise Exception('Coordinates must be positive!')
+    ...
+    >>> p = PositivePoint(1, 2)
+    >>> p.set(x=3)
+    PositivePoint(x=3, y=2)
+    >>> p.set(y=-3)
+    Traceback (most recent call last):
+    Exception: Coordinates must be positive!
+
+    The persistent class also supports the notion of frozen members. The value of a frozen member
+    cannot be updated. For example it could be used to implement an ID that should remain the same
+    over time. A frozen member is denoted by a trailing underscore.
+
+    >>> Point = immutable('x, y, id_', name='Point')
+    >>> p = Point(1, 2, id_=17)
+    >>> p.set(x=3)
+    Point(x=3, y=2, id_=17)
+    >>> p.set(id_=18)
+    Traceback (most recent call last):
+    AttributeError: Cannot set frozen members id_
+    """
+
+    if isinstance(members, six.string_types):
+        members = members.replace(',', ' ').split()
+
+    def frozen_member_test():
+        frozen_members = ["'%s'" % f for f in members if f.endswith('_')]
+        if frozen_members:
+            return """
+        frozen_fields = fields_to_modify & set([{frozen_members}])
+        if frozen_fields:
+            raise AttributeError('Cannot set frozen members %s' % ', '.join(frozen_fields))
+            """.format(frozen_members=', '.join(frozen_members))
+
+        return ''
+
+    verbose_string = ""
+    if sys.version_info < (3, 7):
+        # Verbose is no longer supported in Python 3.7
+        verbose_string = ", verbose={verbose}".format(verbose=verbose)
+
+    quoted_members = ', '.join("'%s'" % m for m in members)
+    template = """
+class {class_name}(namedtuple('ImmutableBase', [{quoted_members}]{verbose_string})):
+    __slots__ = tuple()
+
+    def __repr__(self):
+        return super({class_name}, self).__repr__().replace('ImmutableBase', self.__class__.__name__)
+
+    def set(self, **kwargs):
+        if not kwargs:
+            return self
+
+        fields_to_modify = set(kwargs.keys())
+        if not fields_to_modify <= {member_set}:
+            raise AttributeError("'%s' is not a member" % ', '.join(fields_to_modify - {member_set}))
+
+        {frozen_member_test}
+
+        return self.__class__.__new__(self.__class__, *map(kwargs.pop, [{quoted_members}], self))
+""".format(quoted_members=quoted_members,
+               member_set="set([%s])" % quoted_members if quoted_members else 'set()',
+               frozen_member_test=frozen_member_test(),
+               verbose_string=verbose_string,
+               class_name=name)
+
+    if verbose:
+        print(template)
+
+    from collections import namedtuple
+    namespace = dict(namedtuple=namedtuple, __name__='pyrsistent_immutable')
+    try:
+        six.exec_(template, namespace)
+    except SyntaxError as e:
+        raise SyntaxError(e.message + ':\n' + template)
+
+    return namespace[name]
\ No newline at end of file
diff --git a/third_party/python/pyrsistent/pyrsistent/_pbag.py b/third_party/python/pyrsistent/pyrsistent/_pbag.py
new file mode 100644
index 0000000000..9905e9a6e3
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pbag.py
@@ -0,0 +1,267 @@
+from ._compat import Container, Iterable, Sized, Hashable
+from functools import reduce
+from pyrsistent._pmap import pmap
+
+
+def _add_to_counters(counters, element):
+    return counters.set(element, counters.get(element, 0) + 1)
+
+
+class PBag(object):
+    """
+    A persistent bag/multiset type.
+
+    Requires elements to be hashable, and allows duplicates, but has no
+    ordering. Bags are hashable.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`b`
+    or :py:func:`pbag` to create an instance.
+
+    Some examples:
+
+    >>> s = pbag([1, 2, 3, 1])
+    >>> s2 = s.add(4)
+    >>> s3 = s2.remove(1)
+    >>> s
+    pbag([1, 1, 2, 3])
+    >>> s2
+    pbag([1, 1, 2, 3, 4])
+    >>> s3
+    pbag([1, 2, 3, 4])
+    """
+
+    __slots__ = ('_counts', '__weakref__')
+
+    def __init__(self, counts):
+        self._counts = counts
+
+    def add(self, element):
+        """
+        Add an element to the bag.
+
+        >>> s = pbag([1])
+        >>> s2 = s.add(1)
+        >>> s3 = s.add(2)
+        >>> s2
+        pbag([1, 1])
+        >>> s3
+        pbag([1, 2])
+        """
+        return PBag(_add_to_counters(self._counts, element))
+
+    def update(self, iterable):
+        """
+        Update bag with all elements in iterable.
+
+        >>> s = pbag([1])
+        >>> s.update([1, 2])
+        pbag([1, 1, 2])
+        """
+        if iterable:
+            return PBag(reduce(_add_to_counters, iterable, self._counts))
+
+        return self
+
+    def remove(self, element):
+        """
+        Remove an element from the bag.
+
+        >>> s = pbag([1, 1, 2])
+        >>> s2 = s.remove(1)
+        >>> s3 = s.remove(2)
+        >>> s2
+        pbag([1, 2])
+        >>> s3
+        pbag([1, 1])
+        """
+        if element not in self._counts:
+            raise KeyError(element)
+        elif self._counts[element] == 1:
+            newc = self._counts.remove(element)
+        else:
+            newc = self._counts.set(element, self._counts[element] - 1)
+        return PBag(newc)
+
+    def count(self, element):
+        """
+        Return the number of times an element appears.
+
+
+        >>> pbag([]).count('non-existent')
+        0
+        >>> pbag([1, 1, 2]).count(1)
+        2
+        """
+        return self._counts.get(element, 0)
+
+    def __len__(self):
+        """
+        Return the length including duplicates.
+
+        >>> len(pbag([1, 1, 2]))
+        3
+        """
+        return sum(self._counts.itervalues())
+
+    def __iter__(self):
+        """
+        Return an iterator of all elements, including duplicates.
+
+        >>> list(pbag([1, 1, 2]))
+        [1, 1, 2]
+        >>> list(pbag([1, 2]))
+        [1, 2]
+        """
+        for elt, count in self._counts.iteritems():
+            for i in range(count):
+                yield elt
+
+    def __contains__(self, elt):
+        """
+        Check if an element is in the bag.
+
+        >>> 1 in pbag([1, 1, 2])
+        True
+        >>> 0 in pbag([1, 2])
+        False
+        """
+        return elt in self._counts
+
+    def __repr__(self):
+        return "pbag({0})".format(list(self))
+
+    def __eq__(self, other):
+        """
+        Check if two bags are equivalent, honoring the number of duplicates,
+        and ignoring insertion order.
+
+        >>> pbag([1, 1, 2]) == pbag([1, 2])
+        False
+        >>> pbag([2, 1, 0]) == pbag([0, 1, 2])
+        True
+        """
+        if type(other) is not PBag:
+            raise TypeError("Can only compare PBag with PBags")
+        return self._counts == other._counts
+
+    def __lt__(self, other):
+        raise TypeError('PBags are not orderable')
+
+    __le__ = __lt__
+    __gt__ = __lt__
+    __ge__ = __lt__
+
+    # Multiset-style operations similar to collections.Counter
+
+    def __add__(self, other):
+        """ 
+        Combine elements from two PBags.
+
+        >>> pbag([1, 2, 2]) + pbag([2, 3, 3])
+        pbag([1, 2, 2, 2, 3, 3])
+        """
+        if not isinstance(other, PBag):
+            return NotImplemented
+        result = self._counts.evolver()
+        for elem, other_count in other._counts.iteritems():
+            result[elem] = self.count(elem) + other_count
+        return PBag(result.persistent())
+
+    def __sub__(self, other):
+        """ 
+        Remove elements from one PBag that are present in another.
+
+        >>> pbag([1, 2, 2, 2, 3]) - pbag([2, 3, 3, 4])
+        pbag([1, 2, 2])
+        """
+        if not isinstance(other, PBag):
+            return NotImplemented
+        result = self._counts.evolver()
+        for elem, other_count in other._counts.iteritems():
+            newcount = self.count(elem) - other_count
+            if newcount > 0:
+                result[elem] = newcount
+            elif elem in self:
+                result.remove(elem)
+        return PBag(result.persistent())
+        
+    def __or__(self, other):
+        """ 
+        Union: Keep elements that are present in either of two PBags.
+
+        >>> pbag([1, 2, 2, 2]) | pbag([2, 3, 3])
+        pbag([1, 2, 2, 2, 3, 3])
+        """
+        if not isinstance(other, PBag):
+            return NotImplemented
+        result = self._counts.evolver()
+        for elem, other_count in other._counts.iteritems():
+            count = self.count(elem)
+            newcount = max(count, other_count)
+            result[elem] = newcount
+        return PBag(result.persistent())
+        
+    def __and__(self, other):
+        """
+        Intersection: Only keep elements that are present in both PBags.
+        
+        >>> pbag([1, 2, 2, 2]) & pbag([2, 3, 3])
+        pbag([2])
+        """
+        if not isinstance(other, PBag):
+            return NotImplemented
+        result = pmap().evolver()
+        for elem, count in self._counts.iteritems():
+            newcount = min(count, other.count(elem))
+            if newcount > 0:
+                result[elem] = newcount
+        return PBag(result.persistent())
+    
+    def __hash__(self):
+        """
+        Hash based on value of elements.
+
+        >>> m = pmap({pbag([1, 2]): "it's here!"})
+        >>> m[pbag([2, 1])]
+        "it's here!"
+        >>> pbag([1, 1, 2]) in m
+        False
+        """
+        return hash(self._counts)
+
+
+Container.register(PBag)
+Iterable.register(PBag)
+Sized.register(PBag)
+Hashable.register(PBag)
+
+
+def b(*elements):
+    """
+    Construct a persistent bag.
+
+    Takes an arbitrary number of arguments to insert into the new persistent
+    bag.
+
+    >>> b(1, 2, 3, 2)
+    pbag([1, 2, 2, 3])
+    """
+    return pbag(elements)
+
+
+def pbag(elements):
+    """
+    Convert an iterable to a persistent bag.
+
+    Takes an iterable with elements to insert.
+
+    >>> pbag([1, 2, 3, 2])
+    pbag([1, 2, 2, 3])
+    """
+    if not elements:
+        return _EMPTY_PBAG
+    return PBag(reduce(_add_to_counters, elements, pmap()))
+
+
+_EMPTY_PBAG = PBag(pmap())
+
diff --git a/third_party/python/pyrsistent/pyrsistent/_pclass.py b/third_party/python/pyrsistent/pyrsistent/_pclass.py
new file mode 100644
index 0000000000..a437f71648
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pclass.py
@@ -0,0 +1,264 @@
+import six
+from pyrsistent._checked_types import (InvariantException, CheckedType, _restore_pickle, store_invariants)
+from pyrsistent._field_common import (
+    set_fields, check_type, is_field_ignore_extra_complaint, PFIELD_NO_INITIAL, serialize, check_global_invariants
+)
+from pyrsistent._transformations import transform
+
+
+def _is_pclass(bases):
+    return len(bases) == 1 and bases[0] == CheckedType
+
+
+class PClassMeta(type):
+    def __new__(mcs, name, bases, dct):
+        set_fields(dct, bases, name='_pclass_fields')
+        store_invariants(dct, bases, '_pclass_invariants', '__invariant__')
+        dct['__slots__'] = ('_pclass_frozen',) + tuple(key for key in dct['_pclass_fields'])
+
+        # There must only be one __weakref__ entry in the inheritance hierarchy,
+        # lets put it on the top level class.
+        if _is_pclass(bases):
+            dct['__slots__'] += ('__weakref__',)
+
+        return super(PClassMeta, mcs).__new__(mcs, name, bases, dct)
+
+_MISSING_VALUE = object()
+
+
+def _check_and_set_attr(cls, field, name, value, result, invariant_errors):
+    check_type(cls, field, name, value)
+    is_ok, error_code = field.invariant(value)
+    if not is_ok:
+        invariant_errors.append(error_code)
+    else:
+        setattr(result, name, value)
+
+
+@six.add_metaclass(PClassMeta)
+class PClass(CheckedType):
+    """
+    A PClass is a python class with a fixed set of specified fields. PClasses are declared as python classes inheriting
+    from PClass. It is defined the same way that PRecords are and behaves like a PRecord in all aspects except that it
+    is not a PMap and hence not a collection but rather a plain Python object.
+
+
+    More documentation and examples of PClass usage is available at https://github.com/tobgu/pyrsistent
+    """
+    def __new__(cls, **kwargs):    # Support *args?
+        result = super(PClass, cls).__new__(cls)
+        factory_fields = kwargs.pop('_factory_fields', None)
+        ignore_extra = kwargs.pop('ignore_extra', None)
+        missing_fields = []
+        invariant_errors = []
+        for name, field in cls._pclass_fields.items():
+            if name in kwargs:
+                if factory_fields is None or name in factory_fields:
+                    if is_field_ignore_extra_complaint(PClass, field, ignore_extra):
+                        value = field.factory(kwargs[name], ignore_extra=ignore_extra)
+                    else:
+                        value = field.factory(kwargs[name])
+                else:
+                    value = kwargs[name]
+                _check_and_set_attr(cls, field, name, value, result, invariant_errors)
+                del kwargs[name]
+            elif field.initial is not PFIELD_NO_INITIAL:
+                initial = field.initial() if callable(field.initial) else field.initial
+                _check_and_set_attr(
+                    cls, field, name, initial, result, invariant_errors)
+            elif field.mandatory:
+                missing_fields.append('{0}.{1}'.format(cls.__name__, name))
+
+        if invariant_errors or missing_fields:
+            raise InvariantException(tuple(invariant_errors), tuple(missing_fields), 'Field invariant failed')
+
+        if kwargs:
+            raise AttributeError("'{0}' are not among the specified fields for {1}".format(
+                ', '.join(kwargs), cls.__name__))
+
+        check_global_invariants(result, cls._pclass_invariants)
+
+        result._pclass_frozen = True
+        return result
+
+    def set(self, *args, **kwargs):
+        """
+        Set a field in the instance. Returns a new instance with the updated value. The original instance remains
+        unmodified. Accepts key-value pairs or single string representing the field name and a value.
+
+        >>> from pyrsistent import PClass, field
+        >>> class AClass(PClass):
+        ...     x = field()
+        ...
+        >>> a = AClass(x=1)
+        >>> a2 = a.set(x=2)
+        >>> a3 = a.set('x', 3)
+        >>> a
+        AClass(x=1)
+        >>> a2
+        AClass(x=2)
+        >>> a3
+        AClass(x=3)
+        """
+        if args:
+            kwargs[args[0]] = args[1]
+
+        factory_fields = set(kwargs)
+
+        for key in self._pclass_fields:
+            if key not in kwargs:
+                value = getattr(self, key, _MISSING_VALUE)
+                if value is not _MISSING_VALUE:
+                    kwargs[key] = value
+
+        return self.__class__(_factory_fields=factory_fields, **kwargs)
+
+    @classmethod
+    def create(cls, kwargs, _factory_fields=None, ignore_extra=False):
+        """
+        Factory method. Will create a new PClass of the current type and assign the values
+        specified in kwargs.
+
+        :param ignore_extra: A boolean which when set to True will ignore any keys which appear in kwargs that are not
+                             in the set of fields on the PClass.
+        """
+        if isinstance(kwargs, cls):
+            return kwargs
+
+        if ignore_extra:
+            kwargs = {k: kwargs[k] for k in cls._pclass_fields if k in kwargs}
+
+        return cls(_factory_fields=_factory_fields, ignore_extra=ignore_extra, **kwargs)
+
+    def serialize(self, format=None):
+        """
+        Serialize the current PClass using custom serializer functions for fields where
+        such have been supplied.
+        """
+        result = {}
+        for name in self._pclass_fields:
+            value = getattr(self, name, _MISSING_VALUE)
+            if value is not _MISSING_VALUE:
+                result[name] = serialize(self._pclass_fields[name].serializer, format, value)
+
+        return result
+
+    def transform(self, *transformations):
+        """
+        Apply transformations to the currency PClass. For more details on transformations see
+        the documentation for PMap. Transformations on PClasses do not support key matching
+        since the PClass is not a collection. Apart from that the transformations available
+        for other persistent types work as expected.
+        """
+        return transform(self, transformations)
+
+    def __eq__(self, other):
+        if isinstance(other, self.__class__):
+            for name in self._pclass_fields:
+                if getattr(self, name, _MISSING_VALUE) != getattr(other, name, _MISSING_VALUE):
+                    return False
+
+            return True
+
+        return NotImplemented
+
+    def __ne__(self, other):
+        return not self == other
+
+    def __hash__(self):
+        # May want to optimize this by caching the hash somehow
+        return hash(tuple((key, getattr(self, key, _MISSING_VALUE)) for key in self._pclass_fields))
+
+    def __setattr__(self, key, value):
+        if getattr(self, '_pclass_frozen', False):
+            raise AttributeError("Can't set attribute, key={0}, value={1}".format(key, value))
+
+        super(PClass, self).__setattr__(key, value)
+
+    def __delattr__(self, key):
+            raise AttributeError("Can't delete attribute, key={0}, use remove()".format(key))
+
+    def _to_dict(self):
+        result = {}
+        for key in self._pclass_fields:
+            value = getattr(self, key, _MISSING_VALUE)
+            if value is not _MISSING_VALUE:
+                result[key] = value
+
+        return result
+
+    def __repr__(self):
+        return "{0}({1})".format(self.__class__.__name__,
+                                 ', '.join('{0}={1}'.format(k, repr(v)) for k, v in self._to_dict().items()))
+
+    def __reduce__(self):
+        # Pickling support
+        data = dict((key, getattr(self, key)) for key in self._pclass_fields if hasattr(self, key))
+        return _restore_pickle, (self.__class__, data,)
+
+    def evolver(self):
+        """
+        Returns an evolver for this object.
+        """
+        return _PClassEvolver(self, self._to_dict())
+
+    def remove(self, name):
+        """
+        Remove attribute given by name from the current instance. Raises AttributeError if the
+        attribute doesn't exist.
+        """
+        evolver = self.evolver()
+        del evolver[name]
+        return evolver.persistent()
+
+
+class _PClassEvolver(object):
+    __slots__ = ('_pclass_evolver_original', '_pclass_evolver_data', '_pclass_evolver_data_is_dirty', '_factory_fields')
+
+    def __init__(self, original, initial_dict):
+        self._pclass_evolver_original = original
+        self._pclass_evolver_data = initial_dict
+        self._pclass_evolver_data_is_dirty = False
+        self._factory_fields = set()
+
+    def __getitem__(self, item):
+        return self._pclass_evolver_data[item]
+
+    def set(self, key, value):
+        if self._pclass_evolver_data.get(key, _MISSING_VALUE) is not value:
+            self._pclass_evolver_data[key] = value
+            self._factory_fields.add(key)
+            self._pclass_evolver_data_is_dirty = True
+
+        return self
+
+    def __setitem__(self, key, value):
+        self.set(key, value)
+
+    def remove(self, item):
+        if item in self._pclass_evolver_data:
+            del self._pclass_evolver_data[item]
+            self._factory_fields.discard(item)
+            self._pclass_evolver_data_is_dirty = True
+            return self
+
+        raise AttributeError(item)
+
+    def __delitem__(self, item):
+        self.remove(item)
+
+    def persistent(self):
+        if self._pclass_evolver_data_is_dirty:
+            return self._pclass_evolver_original.__class__(_factory_fields=self._factory_fields,
+                                                           **self._pclass_evolver_data)
+
+        return self._pclass_evolver_original
+
+    def __setattr__(self, key, value):
+        if key not in self.__slots__:
+            self.set(key, value)
+        else:
+            super(_PClassEvolver, self).__setattr__(key, value)
+
+    def __getattr__(self, item):
+        return self[item]
diff --git a/third_party/python/pyrsistent/pyrsistent/_pdeque.py b/third_party/python/pyrsistent/pyrsistent/_pdeque.py
new file mode 100644
index 0000000000..5147b3fa6a
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pdeque.py
@@ -0,0 +1,376 @@
+from ._compat import Sequence, Hashable
+from itertools import islice, chain
+from numbers import Integral
+from pyrsistent._plist import plist
+
+
+class PDeque(object):
+    """
+    Persistent double ended queue (deque). Allows quick appends and pops in both ends. Implemented
+    using two persistent lists.
+
+    A maximum length can be specified to create a bounded queue.
+
+    Fully supports the Sequence and Hashable protocols including indexing and slicing but
+    if you need fast random access go for the PVector instead.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`dq` or :py:func:`pdeque` to
+    create an instance.
+
+    Some examples:
+
+    >>> x = pdeque([1, 2, 3])
+    >>> x.left
+    1
+    >>> x.right
+    3
+    >>> x[0] == x.left
+    True
+    >>> x[-1] == x.right
+    True
+    >>> x.pop()
+    pdeque([1, 2])
+    >>> x.pop() == x[:-1]
+    True
+    >>> x.popleft()
+    pdeque([2, 3])
+    >>> x.append(4)
+    pdeque([1, 2, 3, 4])
+    >>> x.appendleft(4)
+    pdeque([4, 1, 2, 3])
+
+    >>> y = pdeque([1, 2, 3], maxlen=3)
+    >>> y.append(4)
+    pdeque([2, 3, 4], maxlen=3)
+    >>> y.appendleft(4)
+    pdeque([4, 1, 2], maxlen=3)
+    """
+    __slots__ = ('_left_list', '_right_list', '_length', '_maxlen', '__weakref__')
+
+    def __new__(cls, left_list, right_list, length, maxlen=None):
+        instance = super(PDeque, cls).__new__(cls)
+        instance._left_list = left_list
+        instance._right_list = right_list
+        instance._length = length
+
+        if maxlen is not None:
+            if not isinstance(maxlen, Integral):
+                raise TypeError('An integer is required as maxlen')
+
+            if maxlen < 0:
+                raise ValueError("maxlen must be non-negative")
+
+        instance._maxlen = maxlen
+        return instance
+
+    @property
+    def right(self):
+        """
+        Rightmost element in dqueue.
+        """
+        return PDeque._tip_from_lists(self._right_list, self._left_list)
+
+    @property
+    def left(self):
+        """
+        Leftmost element in dqueue.
+        """
+        return PDeque._tip_from_lists(self._left_list, self._right_list)
+
+    @staticmethod
+    def _tip_from_lists(primary_list, secondary_list):
+        if primary_list:
+            return primary_list.first
+
+        if secondary_list:
+            return secondary_list[-1]
+
+        raise IndexError('No elements in empty deque')
+
+    def __iter__(self):
+        return chain(self._left_list, self._right_list.reverse())
+
+    def __repr__(self):
+        return "pdeque({0}{1})".format(list(self),
+                                       ', maxlen={0}'.format(self._maxlen) if self._maxlen is not None else '')
+    __str__ = __repr__
+
+    @property
+    def maxlen(self):
+        """
+        Maximum length of the queue.
+        """
+        return self._maxlen
+
+    def pop(self, count=1):
+        """
+        Return new deque with rightmost element removed. Popping the empty queue
+        will return the empty queue. A optional count can be given to indicate the
+        number of elements to pop. Popping with a negative index is the same as
+        popleft. Executes in amortized O(k) where k is the number of elements to pop.
+
+        >>> pdeque([1, 2]).pop()
+        pdeque([1])
+        >>> pdeque([1, 2]).pop(2)
+        pdeque([])
+        >>> pdeque([1, 2]).pop(-1)
+        pdeque([2])
+        """
+        if count < 0:
+            return self.popleft(-count)
+
+        new_right_list, new_left_list = PDeque._pop_lists(self._right_list, self._left_list, count)
+        return PDeque(new_left_list, new_right_list, max(self._length - count, 0), self._maxlen)
+
+    def popleft(self, count=1):
+        """
+        Return new deque with leftmost element removed. Otherwise functionally
+        equivalent to pop().
+
+        >>> pdeque([1, 2]).popleft()
+        pdeque([2])
+        """
+        if count < 0:
+            return self.pop(-count)
+
+        new_left_list, new_right_list = PDeque._pop_lists(self._left_list, self._right_list, count)
+        return PDeque(new_left_list, new_right_list, max(self._length - count, 0), self._maxlen)
+
+    @staticmethod
+    def _pop_lists(primary_list, secondary_list, count):
+        new_primary_list = primary_list
+        new_secondary_list = secondary_list
+
+        while count > 0 and (new_primary_list or new_secondary_list):
+            count -= 1
+            if new_primary_list.rest:
+                new_primary_list = new_primary_list.rest
+            elif new_primary_list:
+                new_primary_list = new_secondary_list.reverse()
+                new_secondary_list = plist()
+            else:
+                new_primary_list = new_secondary_list.reverse().rest
+                new_secondary_list = plist()
+
+        return new_primary_list, new_secondary_list
+
+    def _is_empty(self):
+        return not self._left_list and not self._right_list
+
+    def __lt__(self, other):
+        if not isinstance(other, PDeque):
+            return NotImplemented
+
+        return tuple(self) < tuple(other)
+
+    def __eq__(self, other):
+        if not isinstance(other, PDeque):
+            return NotImplemented
+
+        if tuple(self) == tuple(other):
+            # Sanity check of the length value since it is redundant (there for performance)
+            assert len(self) == len(other)
+            return True
+
+        return False
+
+    def __hash__(self):
+        return  hash(tuple(self))
+
+    def __len__(self):
+        return self._length
+
+    def append(self, elem):
+        """
+        Return new deque with elem as the rightmost element.
+
+        >>> pdeque([1, 2]).append(3)
+        pdeque([1, 2, 3])
+        """
+        new_left_list, new_right_list, new_length = self._append(self._left_list, self._right_list, elem)
+        return PDeque(new_left_list, new_right_list, new_length, self._maxlen)
+
+    def appendleft(self, elem):
+        """
+        Return new deque with elem as the leftmost element.
+
+        >>> pdeque([1, 2]).appendleft(3)
+        pdeque([3, 1, 2])
+        """
+        new_right_list, new_left_list, new_length = self._append(self._right_list, self._left_list, elem)
+        return PDeque(new_left_list, new_right_list, new_length, self._maxlen)
+
+    def _append(self, primary_list, secondary_list, elem):
+        if self._maxlen is not None and self._length == self._maxlen:
+            if self._maxlen == 0:
+                return primary_list, secondary_list, 0
+            new_primary_list, new_secondary_list = PDeque._pop_lists(primary_list, secondary_list, 1)
+            return new_primary_list, new_secondary_list.cons(elem), self._length
+
+        return primary_list, secondary_list.cons(elem), self._length + 1
+
+    @staticmethod
+    def _extend_list(the_list, iterable):
+        count = 0
+        for elem in iterable:
+            the_list = the_list.cons(elem)
+            count += 1
+
+        return the_list, count
+
+    def _extend(self, primary_list, secondary_list, iterable):
+        new_primary_list, extend_count = PDeque._extend_list(primary_list, iterable)
+        new_secondary_list = secondary_list
+        current_len = self._length + extend_count
+        if self._maxlen is not None and current_len > self._maxlen:
+            pop_len = current_len - self._maxlen
+            new_secondary_list, new_primary_list = PDeque._pop_lists(new_secondary_list, new_primary_list, pop_len)
+            extend_count -= pop_len
+
+        return new_primary_list, new_secondary_list, extend_count
+
+    def extend(self, iterable):
+        """
+        Return new deque with all elements of iterable appended to the right.
+
+        >>> pdeque([1, 2]).extend([3, 4])
+        pdeque([1, 2, 3, 4])
+        """
+        new_right_list, new_left_list, extend_count = self._extend(self._right_list, self._left_list, iterable)
+        return PDeque(new_left_list, new_right_list, self._length + extend_count, self._maxlen)
+
+    def extendleft(self, iterable):
+        """
+        Return new deque with all elements of iterable appended to the left.
+
+        NB! The elements will be inserted in reverse order compared to the order in the iterable.
+
+        >>> pdeque([1, 2]).extendleft([3, 4])
+        pdeque([4, 3, 1, 2])
+        """
+        new_left_list, new_right_list, extend_count = self._extend(self._left_list, self._right_list, iterable)
+        return PDeque(new_left_list, new_right_list, self._length + extend_count, self._maxlen)
+
+    def count(self, elem):
+        """
+        Return the number of elements equal to elem present in the queue
+
+        >>> pdeque([1, 2, 1]).count(1)
+        2
+        """
+        return self._left_list.count(elem) + self._right_list.count(elem)
+
+    def remove(self, elem):
+        """
+        Return new deque with first element from left equal to elem removed. If no such element is found
+        a ValueError is raised.
+
+        >>> pdeque([2, 1, 2]).remove(2)
+        pdeque([1, 2])
+        """
+        try:
+            return PDeque(self._left_list.remove(elem), self._right_list, self._length - 1)
+        except ValueError:
+            # Value not found in left list, try the right list
+            try:
+                # This is severely inefficient with a double reverse, should perhaps implement a remove_last()?
+                return PDeque(self._left_list,
+                               self._right_list.reverse().remove(elem).reverse(), self._length - 1)
+            except ValueError:
+                raise ValueError('{0} not found in PDeque'.format(elem))
+
+    def reverse(self):
+        """
+        Return reversed deque.
+
+        >>> pdeque([1, 2, 3]).reverse()
+        pdeque([3, 2, 1])
+
+        Also supports the standard python reverse function.
+
+        >>> reversed(pdeque([1, 2, 3]))
+        pdeque([3, 2, 1])
+        """
+        return PDeque(self._right_list, self._left_list, self._length)
+    __reversed__ = reverse
+
+    def rotate(self, steps):
+        """
+        Return deque with elements rotated steps steps.
+
+        >>> x = pdeque([1, 2, 3])
+        >>> x.rotate(1)
+        pdeque([3, 1, 2])
+        >>> x.rotate(-2)
+        pdeque([3, 1, 2])
+        """
+        popped_deque = self.pop(steps)
+        if steps >= 0:
+            return popped_deque.extendleft(islice(self.reverse(), steps))
+
+        return popped_deque.extend(islice(self, -steps))
+
+    def __reduce__(self):
+        # Pickling support
+        return pdeque, (list(self), self._maxlen)
+
+    def __getitem__(self, index):
+        if isinstance(index, slice):
+            if index.step is not None and index.step != 1:
+                # Too difficult, no structural sharing possible
+                return pdeque(tuple(self)[index], maxlen=self._maxlen)
+
+            result = self
+            if index.start is not None:
+                result = result.popleft(index.start % self._length)
+            if index.stop is not None:
+                result = result.pop(self._length - (index.stop % self._length))
+
+            return result
+
+        if not isinstance(index, Integral):
+            raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__)
+
+        if index >= 0:
+            return self.popleft(index).left
+
+        shifted = len(self) + index
+        if shifted < 0:
+            raise IndexError(
+                "pdeque index {0} out of range {1}".format(index, len(self)),
+            )
+        return self.popleft(shifted).left
+
+    index = Sequence.index
+
+Sequence.register(PDeque)
+Hashable.register(PDeque)
+
+
+def pdeque(iterable=(), maxlen=None):
+    """
+    Return deque containing the elements of iterable. If maxlen is specified then
+    len(iterable) - maxlen elements are discarded from the left to if len(iterable) > maxlen.
+
+    >>> pdeque([1, 2, 3])
+    pdeque([1, 2, 3])
+    >>> pdeque([1, 2, 3, 4], maxlen=2)
+    pdeque([3, 4], maxlen=2)
+    """
+    t = tuple(iterable)
+    if maxlen is not None:
+        t = t[-maxlen:]
+    length = len(t)
+    pivot = int(length / 2)
+    left = plist(t[:pivot])
+    right = plist(t[pivot:], reverse=True)
+    return PDeque(left, right, length, maxlen)
+
+def dq(*elements):
+    """
+    Return deque containing all arguments.
+
+    >>> dq(1, 2, 3)
+    pdeque([1, 2, 3])
+    """
+    return pdeque(elements)
diff --git a/third_party/python/pyrsistent/pyrsistent/_plist.py b/third_party/python/pyrsistent/pyrsistent/_plist.py
new file mode 100644
index 0000000000..8b4267f5e3
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_plist.py
@@ -0,0 +1,313 @@
+from ._compat import Sequence, Hashable
+from numbers import Integral
+from functools import reduce
+
+
+class _PListBuilder(object):
+    """
+    Helper class to allow construction of a list without
+    having to reverse it in the end.
+    """
+    __slots__ = ('_head', '_tail')
+
+    def __init__(self):
+        self._head = _EMPTY_PLIST
+        self._tail = _EMPTY_PLIST
+
+    def _append(self, elem, constructor):
+        if not self._tail:
+            self._head = constructor(elem)
+            self._tail = self._head
+        else:
+            self._tail.rest = constructor(elem)
+            self._tail = self._tail.rest
+
+        return self._head
+
+    def append_elem(self, elem):
+        return self._append(elem, lambda e: PList(e, _EMPTY_PLIST))
+
+    def append_plist(self, pl):
+        return self._append(pl, lambda l: l)
+
+    def build(self):
+        return self._head
+
+
+class _PListBase(object):
+    __slots__ = ('__weakref__',)
+
+    # Selected implementations can be taken straight from the Sequence
+    # class, other are less suitable. Especially those that work with
+    # index lookups.
+    count = Sequence.count
+    index = Sequence.index
+
+    def __reduce__(self):
+        # Pickling support
+        return plist, (list(self),)
+
+    def __len__(self):
+        """
+        Return the length of the list, computed by traversing it.
+
+        This is obviously O(n) but with the current implementation
+        where a list is also a node the overhead of storing the length
+        in every node would be quite significant.
+        """
+        return sum(1 for _ in self)
+
+    def __repr__(self):
+        return "plist({0})".format(list(self))
+    __str__ = __repr__
+
+    def cons(self, elem):
+        """
+        Return a new list with elem inserted as new head.
+
+        >>> plist([1, 2]).cons(3)
+        plist([3, 1, 2])
+        """
+        return PList(elem, self)
+
+    def mcons(self, iterable):
+        """
+        Return a new list with all elements of iterable repeatedly cons:ed to the current list.
+        NB! The elements will be inserted in the reverse order of the iterable.
+        Runs in O(len(iterable)).
+
+        >>> plist([1, 2]).mcons([3, 4])
+        plist([4, 3, 1, 2])
+        """
+        head = self
+        for elem in iterable:
+            head = head.cons(elem)
+
+        return head
+
+    def reverse(self):
+        """
+        Return a reversed version of list. Runs in O(n) where n is the length of the list.
+
+        >>> plist([1, 2, 3]).reverse()
+        plist([3, 2, 1])
+
+        Also supports the standard reversed function.
+
+        >>> reversed(plist([1, 2, 3]))
+        plist([3, 2, 1])
+        """
+        result = plist()
+        head = self
+        while head:
+            result = result.cons(head.first)
+            head = head.rest
+
+        return result
+    __reversed__ = reverse
+
+    def split(self, index):
+        """
+        Spilt the list at position specified by index. Returns a tuple containing the
+        list up until index and the list after the index. Runs in O(index).
+
+        >>> plist([1, 2, 3, 4]).split(2)
+        (plist([1, 2]), plist([3, 4]))
+        """
+        lb = _PListBuilder()
+        right_list = self
+        i = 0
+        while right_list and i < index:
+            lb.append_elem(right_list.first)
+            right_list = right_list.rest
+            i += 1
+
+        if not right_list:
+            # Just a small optimization in the cases where no split occurred
+            return self, _EMPTY_PLIST
+
+        return lb.build(), right_list
+
+    def __iter__(self):
+        li = self
+        while li:
+            yield li.first
+            li = li.rest
+
+    def __lt__(self, other):
+        if not isinstance(other, _PListBase):
+            return NotImplemented
+
+        return tuple(self) < tuple(other)
+
+    def __eq__(self, other):
+        """
+        Traverses the lists, checking equality of elements.
+        
+        This is an O(n) operation, but preserves the standard semantics of list equality.
+        """
+        if not isinstance(other, _PListBase):
+            return NotImplemented
+
+        self_head = self
+        other_head = other
+        while self_head and other_head:
+            if not self_head.first == other_head.first:
+                return False
+            self_head = self_head.rest
+            other_head = other_head.rest
+
+        return not self_head and not other_head
+
+    def __getitem__(self, index):
+        # Don't use this this data structure if you plan to do a lot of indexing, it is
+        # very inefficient! Use a PVector instead!
+
+        if isinstance(index, slice):
+            if index.start is not None and index.stop is None and (index.step is None or index.step == 1):
+                return self._drop(index.start)
+
+            # Take the easy way out for all other slicing cases, not much structural reuse possible anyway
+            return plist(tuple(self)[index])
+
+        if not isinstance(index, Integral):
+            raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__)
+
+        if index < 0:
+            # NB: O(n)!
+            index += len(self)
+
+        try:
+            return self._drop(index).first
+        except AttributeError:
+            raise IndexError("PList index out of range")
+
+    def _drop(self, count):
+        if count < 0:
+            raise IndexError("PList index out of range")
+
+        head = self
+        while count > 0:
+            head = head.rest
+            count -= 1
+
+        return head
+
+    def __hash__(self):
+        return hash(tuple(self))
+
+    def remove(self, elem):
+        """
+        Return new list with first element equal to elem removed. O(k) where k is the position
+        of the element that is removed.
+
+        Raises ValueError if no matching element is found.
+
+        >>> plist([1, 2, 1]).remove(1)
+        plist([2, 1])
+        """
+
+        builder = _PListBuilder()
+        head = self
+        while head:
+            if head.first == elem:
+                return builder.append_plist(head.rest)
+
+            builder.append_elem(head.first)
+            head = head.rest
+
+        raise ValueError('{0} not found in PList'.format(elem))
+
+
+class PList(_PListBase):
+    """
+    Classical Lisp style singly linked list. Adding elements to the head using cons is O(1).
+    Element access is O(k) where k is the position of the element in the list. Taking the
+    length of the list is O(n).
+
+    Fully supports the Sequence and Hashable protocols including indexing and slicing but
+    if you need fast random access go for the PVector instead.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`l` or :py:func:`plist` to
+    create an instance.
+
+    Some examples:
+
+    >>> x = plist([1, 2])
+    >>> y = x.cons(3)
+    >>> x
+    plist([1, 2])
+    >>> y
+    plist([3, 1, 2])
+    >>> y.first
+    3
+    >>> y.rest == x
+    True
+    >>> y[:2]
+    plist([3, 1])
+    """
+    __slots__ = ('first', 'rest')
+
+    def __new__(cls, first, rest):
+        instance = super(PList, cls).__new__(cls)
+        instance.first = first
+        instance.rest = rest
+        return instance
+
+    def __bool__(self):
+        return True
+    __nonzero__ = __bool__
+
+
+Sequence.register(PList)
+Hashable.register(PList)
+
+
+class _EmptyPList(_PListBase):
+    __slots__ = ()
+
+    def __bool__(self):
+        return False
+    __nonzero__ = __bool__
+
+    @property
+    def first(self):
+        raise AttributeError("Empty PList has no first")
+
+    @property
+    def rest(self):
+        return self
+
+
+Sequence.register(_EmptyPList)
+Hashable.register(_EmptyPList)
+
+_EMPTY_PLIST = _EmptyPList()
+
+
+def plist(iterable=(), reverse=False):
+    """
+    Creates a new persistent list containing all elements of iterable.
+    Optional parameter reverse specifies if the elements should be inserted in
+    reverse order or not.
+
+    >>> plist([1, 2, 3])
+    plist([1, 2, 3])
+    >>> plist([1, 2, 3], reverse=True)
+    plist([3, 2, 1])
+    """
+    if not reverse:
+        iterable = list(iterable)
+        iterable.reverse()
+
+    return reduce(lambda pl, elem: pl.cons(elem), iterable, _EMPTY_PLIST)
+
+
+def l(*elements):
+    """
+    Creates a new persistent list containing all arguments.
+
+    >>> l(1, 2, 3)
+    plist([1, 2, 3])
+    """
+    return plist(elements)
diff --git a/third_party/python/pyrsistent/pyrsistent/_pmap.py b/third_party/python/pyrsistent/pyrsistent/_pmap.py
new file mode 100644
index 0000000000..e8a0ec53f8
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pmap.py
@@ -0,0 +1,460 @@
+from ._compat import Mapping, Hashable
+from itertools import chain
+import six
+from pyrsistent._pvector import pvector
+from pyrsistent._transformations import transform
+
+
+class PMap(object):
+    """
+    Persistent map/dict. Tries to follow the same naming conventions as the built in dict where feasible.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`m` or :py:func:`pmap` to
+    create an instance.
+
+    Was originally written as a very close copy of the Clojure equivalent but was later rewritten to closer
+    re-assemble the python dict. This means that a sparse vector (a PVector) of buckets is used. The keys are
+    hashed and the elements inserted at position hash % len(bucket_vector). Whenever the map size exceeds 2/3 of
+    the containing vectors size the map is reallocated to a vector of double the size. This is done to avoid
+    excessive hash collisions.
+
+    This structure corresponds most closely to the built in dict type and is intended as a replacement. Where the
+    semantics are the same (more or less) the same function names have been used but for some cases it is not possible,
+    for example assignments and deletion of values.
+
+    PMap implements the Mapping protocol and is Hashable. It also supports dot-notation for
+    element access.
+
+    Random access and insert is log32(n) where n is the size of the map.
+
+    The following are examples of some common operations on persistent maps
+
+    >>> m1 = m(a=1, b=3)
+    >>> m2 = m1.set('c', 3)
+    >>> m3 = m2.remove('a')
+    >>> m1
+    pmap({'b': 3, 'a': 1})
+    >>> m2
+    pmap({'c': 3, 'b': 3, 'a': 1})
+    >>> m3
+    pmap({'c': 3, 'b': 3})
+    >>> m3['c']
+    3
+    >>> m3.c
+    3
+    """
+    __slots__ = ('_size', '_buckets', '__weakref__', '_cached_hash')
+
+    def __new__(cls, size, buckets):
+        self = super(PMap, cls).__new__(cls)
+        self._size = size
+        self._buckets = buckets
+        return self
+
+    @staticmethod
+    def _get_bucket(buckets, key):
+        index = hash(key) % len(buckets)
+        bucket = buckets[index]
+        return index, bucket
+
+    @staticmethod
+    def _getitem(buckets, key):
+        _, bucket = PMap._get_bucket(buckets, key)
+        if bucket:
+            for k, v in bucket:
+                if k == key:
+                    return v
+
+        raise KeyError(key)
+
+    def __getitem__(self, key):
+        return PMap._getitem(self._buckets, key)
+
+    @staticmethod
+    def _contains(buckets, key):
+        _, bucket = PMap._get_bucket(buckets, key)
+        if bucket:
+            for k, _ in bucket:
+                if k == key:
+                    return True
+
+            return False
+
+        return False
+
+    def __contains__(self, key):
+        return self._contains(self._buckets, key)
+
+    get = Mapping.get
+
+    def __iter__(self):
+        return self.iterkeys()
+
+    def __getattr__(self, key):
+        try:
+            return self[key]
+        except KeyError:
+            raise AttributeError(
+                "{0} has no attribute '{1}'".format(type(self).__name__, key)
+            )
+
+    def iterkeys(self):
+        for k, _ in self.iteritems():
+            yield k
+
+    # These are more efficient implementations compared to the original
+    # methods that are based on the keys iterator and then calls the
+    # accessor functions to access the value for the corresponding key
+    def itervalues(self):
+        for _, v in self.iteritems():
+            yield v
+
+    def iteritems(self):
+        for bucket in self._buckets:
+            if bucket:
+                for k, v in bucket:
+                    yield k, v
+
+    def values(self):
+        return pvector(self.itervalues())
+
+    def keys(self):
+        return pvector(self.iterkeys())
+
+    def items(self):
+        return pvector(self.iteritems())
+
+    def __len__(self):
+        return self._size
+
+    def __repr__(self):
+        return 'pmap({0})'.format(str(dict(self)))
+
+    def __eq__(self, other):
+        if self is other:
+            return True
+        if not isinstance(other, Mapping):
+            return NotImplemented
+        if len(self) != len(other):
+            return False
+        if isinstance(other, PMap):
+            if (hasattr(self, '_cached_hash') and hasattr(other, '_cached_hash')
+                    and self._cached_hash != other._cached_hash):
+                return False
+            if self._buckets == other._buckets:
+                return True
+            return dict(self.iteritems()) == dict(other.iteritems())
+        elif isinstance(other, dict):
+            return dict(self.iteritems()) == other
+        return dict(self.iteritems()) == dict(six.iteritems(other))
+
+    __ne__ = Mapping.__ne__
+
+    def __lt__(self, other):
+        raise TypeError('PMaps are not orderable')
+
+    __le__ = __lt__
+    __gt__ = __lt__
+    __ge__ = __lt__
+
+    def __str__(self):
+        return self.__repr__()
+
+    def __hash__(self):
+        if not hasattr(self, '_cached_hash'):
+            self._cached_hash = hash(frozenset(self.iteritems()))
+        return self._cached_hash
+
+    def set(self, key, val):
+        """
+        Return a new PMap with key and val inserted.
+
+        >>> m1 = m(a=1, b=2)
+        >>> m2 = m1.set('a', 3)
+        >>> m3 = m1.set('c' ,4)
+        >>> m1
+        pmap({'b': 2, 'a': 1})
+        >>> m2
+        pmap({'b': 2, 'a': 3})
+        >>> m3
+        pmap({'c': 4, 'b': 2, 'a': 1})
+        """
+        return self.evolver().set(key, val).persistent()
+
+    def remove(self, key):
+        """
+        Return a new PMap without the element specified by key. Raises KeyError if the element
+        is not present.
+
+        >>> m1 = m(a=1, b=2)
+        >>> m1.remove('a')
+        pmap({'b': 2})
+        """
+        return self.evolver().remove(key).persistent()
+
+    def discard(self, key):
+        """
+        Return a new PMap without the element specified by key. Returns reference to itself
+        if element is not present.
+
+        >>> m1 = m(a=1, b=2)
+        >>> m1.discard('a')
+        pmap({'b': 2})
+        >>> m1 is m1.discard('c')
+        True
+        """
+        try:
+            return self.remove(key)
+        except KeyError:
+            return self
+
+    def update(self, *maps):
+        """
+        Return a new PMap with the items in Mappings inserted. If the same key is present in multiple
+        maps the rightmost (last) value is inserted.
+
+        >>> m1 = m(a=1, b=2)
+        >>> m1.update(m(a=2, c=3), {'a': 17, 'd': 35})
+        pmap({'c': 3, 'b': 2, 'a': 17, 'd': 35})
+        """
+        return self.update_with(lambda l, r: r, *maps)
+
+    def update_with(self, update_fn, *maps):
+        """
+        Return a new PMap with the items in Mappings maps inserted. If the same key is present in multiple
+        maps the values will be merged using merge_fn going from left to right.
+
+        >>> from operator import add
+        >>> m1 = m(a=1, b=2)
+        >>> m1.update_with(add, m(a=2))
+        pmap({'b': 2, 'a': 3})
+
+        The reverse behaviour of the regular merge. Keep the leftmost element instead of the rightmost.
+
+        >>> m1 = m(a=1)
+        >>> m1.update_with(lambda l, r: l, m(a=2), {'a':3})
+        pmap({'a': 1})
+        """
+        evolver = self.evolver()
+        for map in maps:
+            for key, value in map.items():
+                evolver.set(key, update_fn(evolver[key], value) if key in evolver else value)
+
+        return evolver.persistent()
+
+    def __add__(self, other):
+        return self.update(other)
+
+    def __reduce__(self):
+        # Pickling support
+        return pmap, (dict(self),)
+
+    def transform(self, *transformations):
+        """
+        Transform arbitrarily complex combinations of PVectors and PMaps. A transformation
+        consists of two parts. One match expression that specifies which elements to transform
+        and one transformation function that performs the actual transformation.
+
+        >>> from pyrsistent import freeze, ny
+        >>> news_paper = freeze({'articles': [{'author': 'Sara', 'content': 'A short article'},
+        ...                                   {'author': 'Steve', 'content': 'A slightly longer article'}],
+        ...                      'weather': {'temperature': '11C', 'wind': '5m/s'}})
+        >>> short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:25] + '...' if len(c) > 25 else c)
+        >>> very_short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:15] + '...' if len(c) > 15 else c)
+        >>> very_short_news.articles[0].content
+        'A short article'
+        >>> very_short_news.articles[1].content
+        'A slightly long...'
+
+        When nothing has been transformed the original data structure is kept
+
+        >>> short_news is news_paper
+        True
+        >>> very_short_news is news_paper
+        False
+        >>> very_short_news.articles[0] is news_paper.articles[0]
+        True
+        """
+        return transform(self, transformations)
+
+    def copy(self):
+        return self
+
+    class _Evolver(object):
+        __slots__ = ('_buckets_evolver', '_size', '_original_pmap')
+
+        def __init__(self, original_pmap):
+            self._original_pmap = original_pmap
+            self._buckets_evolver = original_pmap._buckets.evolver()
+            self._size = original_pmap._size
+
+        def __getitem__(self, key):
+            return PMap._getitem(self._buckets_evolver, key)
+
+        def __setitem__(self, key, val):
+            self.set(key, val)
+
+        def set(self, key, val):
+            if len(self._buckets_evolver) < 0.67 * self._size:
+                self._reallocate(2 * len(self._buckets_evolver))
+
+            kv = (key, val)
+            index, bucket = PMap._get_bucket(self._buckets_evolver, key)
+            if bucket:
+                for k, v in bucket:
+                    if k == key:
+                        if v is not val:
+                            new_bucket = [(k2, v2) if k2 != k else (k2, val) for k2, v2 in bucket]
+                            self._buckets_evolver[index] = new_bucket
+
+                        return self
+
+                new_bucket = [kv]
+                new_bucket.extend(bucket)
+                self._buckets_evolver[index] = new_bucket
+                self._size += 1
+            else:
+                self._buckets_evolver[index] = [kv]
+                self._size += 1
+
+            return self
+
+        def _reallocate(self, new_size):
+            new_list = new_size * [None]
+            buckets = self._buckets_evolver.persistent()
+            for k, v in chain.from_iterable(x for x in buckets if x):
+                index = hash(k) % new_size
+                if new_list[index]:
+                    new_list[index].append((k, v))
+                else:
+                    new_list[index] = [(k, v)]
+
+            # A reallocation should always result in a dirty buckets evolver to avoid
+            # possible loss of elements when doing the reallocation.
+            self._buckets_evolver = pvector().evolver()
+            self._buckets_evolver.extend(new_list)
+
+        def is_dirty(self):
+            return self._buckets_evolver.is_dirty()
+
+        def persistent(self):
+            if self.is_dirty():
+                self._original_pmap = PMap(self._size, self._buckets_evolver.persistent())
+
+            return self._original_pmap
+
+        def __len__(self):
+            return self._size
+
+        def __contains__(self, key):
+            return PMap._contains(self._buckets_evolver, key)
+
+        def __delitem__(self, key):
+            self.remove(key)
+
+        def remove(self, key):
+            index, bucket = PMap._get_bucket(self._buckets_evolver, key)
+
+            if bucket:
+                new_bucket = [(k, v) for (k, v) in bucket if k != key]
+                if len(bucket) > len(new_bucket):
+                    self._buckets_evolver[index] = new_bucket if new_bucket else None
+                    self._size -= 1
+                    return self
+
+            raise KeyError('{0}'.format(key))
+
+    def evolver(self):
+        """
+        Create a new evolver for this pmap. For a discussion on evolvers in general see the
+        documentation for the pvector evolver.
+
+        Create the evolver and perform various mutating updates to it:
+
+        >>> m1 = m(a=1, b=2)
+        >>> e = m1.evolver()
+        >>> e['c'] = 3
+        >>> len(e)
+        3
+        >>> del e['a']
+
+        The underlying pmap remains the same:
+
+        >>> m1
+        pmap({'b': 2, 'a': 1})
+
+        The changes are kept in the evolver. An updated pmap can be created using the
+        persistent() function on the evolver.
+
+        >>> m2 = e.persistent()
+        >>> m2
+        pmap({'c': 3, 'b': 2})
+
+        The new pmap will share data with the original pmap in the same way that would have
+        been done if only using operations on the pmap.
+        """
+        return self._Evolver(self)
+
+Mapping.register(PMap)
+Hashable.register(PMap)
+
+
+def _turbo_mapping(initial, pre_size):
+    if pre_size:
+        size = pre_size
+    else:
+        try:
+            size = 2 * len(initial) or 8
+        except Exception:
+            # Guess we can't figure out the length. Give up on length hinting,
+            # we can always reallocate later.
+            size = 8
+
+    buckets = size * [None]
+
+    if not isinstance(initial, Mapping):
+        # Make a dictionary of the initial data if it isn't already,
+        # that will save us some job further down since we can assume no
+        # key collisions
+        initial = dict(initial)
+
+    for k, v in six.iteritems(initial):
+        h = hash(k)
+        index = h % size
+        bucket = buckets[index]
+
+        if bucket:
+            bucket.append((k, v))
+        else:
+            buckets[index] = [(k, v)]
+
+    return PMap(len(initial), pvector().extend(buckets))
+
+
+_EMPTY_PMAP = _turbo_mapping({}, 0)
+
+
+def pmap(initial={}, pre_size=0):
+    """
+    Create new persistent map, inserts all elements in initial into the newly created map.
+    The optional argument pre_size may be used to specify an initial size of the underlying bucket vector. This
+    may have a positive performance impact in the cases where you know beforehand that a large number of elements
+    will be inserted into the map eventually since it will reduce the number of reallocations required.
+
+    >>> pmap({'a': 13, 'b': 14})
+    pmap({'b': 14, 'a': 13})
+    """
+    if not initial:
+        return _EMPTY_PMAP
+
+    return _turbo_mapping(initial, pre_size)
+
+
+def m(**kwargs):
+    """
+    Creates a new persitent map. Inserts all key value arguments into the newly created map.
+
+    >>> m(a=13, b=14)
+    pmap({'b': 14, 'a': 13})
+    """
+    return pmap(kwargs)
diff --git a/third_party/python/pyrsistent/pyrsistent/_precord.py b/third_party/python/pyrsistent/pyrsistent/_precord.py
new file mode 100644
index 0000000000..ec8d32c3da
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_precord.py
@@ -0,0 +1,169 @@
+import six
+from pyrsistent._checked_types import CheckedType, _restore_pickle, InvariantException, store_invariants
+from pyrsistent._field_common import (
+    set_fields, check_type, is_field_ignore_extra_complaint, PFIELD_NO_INITIAL, serialize, check_global_invariants
+)
+from pyrsistent._pmap import PMap, pmap
+
+
+class _PRecordMeta(type):
+    def __new__(mcs, name, bases, dct):
+        set_fields(dct, bases, name='_precord_fields')
+        store_invariants(dct, bases, '_precord_invariants', '__invariant__')
+
+        dct['_precord_mandatory_fields'] = \
+            set(name for name, field in dct['_precord_fields'].items() if field.mandatory)
+
+        dct['_precord_initial_values'] = \
+            dict((k, field.initial) for k, field in dct['_precord_fields'].items() if field.initial is not PFIELD_NO_INITIAL)
+
+
+        dct['__slots__'] = ()
+
+        return super(_PRecordMeta, mcs).__new__(mcs, name, bases, dct)
+
+
+@six.add_metaclass(_PRecordMeta)
+class PRecord(PMap, CheckedType):
+    """
+    A PRecord is a PMap with a fixed set of specified fields. Records are declared as python classes inheriting
+    from PRecord. Because it is a PMap it has full support for all Mapping methods such as iteration and element
+    access using subscript notation.
+
+    More documentation and examples of PRecord usage is available at https://github.com/tobgu/pyrsistent
+    """
+    def __new__(cls, **kwargs):
+        # Hack total! If these two special attributes exist that means we can create
+        # ourselves. Otherwise we need to go through the Evolver to create the structures
+        # for us.
+        if '_precord_size' in kwargs and '_precord_buckets' in kwargs:
+            return super(PRecord, cls).__new__(cls, kwargs['_precord_size'], kwargs['_precord_buckets'])
+
+        factory_fields = kwargs.pop('_factory_fields', None)
+        ignore_extra = kwargs.pop('_ignore_extra', False)
+
+        initial_values = kwargs
+        if cls._precord_initial_values:
+            initial_values = dict((k, v() if callable(v) else v)
+                                  for k, v in cls._precord_initial_values.items())
+            initial_values.update(kwargs)
+
+        e = _PRecordEvolver(cls, pmap(), _factory_fields=factory_fields, _ignore_extra=ignore_extra)
+        for k, v in initial_values.items():
+            e[k] = v
+
+        return e.persistent()
+
+    def set(self, *args, **kwargs):
+        """
+        Set a field in the record. This set function differs slightly from that in the PMap
+        class. First of all it accepts key-value pairs. Second it accepts multiple key-value
+        pairs to perform one, atomic, update of multiple fields.
+        """
+
+        # The PRecord set() can accept kwargs since all fields that have been declared are
+        # valid python identifiers. Also allow multiple fields to be set in one operation.
+        if args:
+            return super(PRecord, self).set(args[0], args[1])
+
+        return self.update(kwargs)
+
+    def evolver(self):
+        """
+        Returns an evolver of this object.
+        """
+        return _PRecordEvolver(self.__class__, self)
+
+    def __repr__(self):
+        return "{0}({1})".format(self.__class__.__name__,
+                                 ', '.join('{0}={1}'.format(k, repr(v)) for k, v in self.items()))
+
+    @classmethod
+    def create(cls, kwargs, _factory_fields=None, ignore_extra=False):
+        """
+        Factory method. Will create a new PRecord of the current type and assign the values
+        specified in kwargs.
+
+        :param ignore_extra: A boolean which when set to True will ignore any keys which appear in kwargs that are not
+                             in the set of fields on the PRecord.
+        """
+        if isinstance(kwargs, cls):
+            return kwargs
+
+        if ignore_extra:
+            kwargs = {k: kwargs[k] for k in cls._precord_fields if k in kwargs}
+
+        return cls(_factory_fields=_factory_fields, _ignore_extra=ignore_extra, **kwargs)
+
+    def __reduce__(self):
+        # Pickling support
+        return _restore_pickle, (self.__class__, dict(self),)
+
+    def serialize(self, format=None):
+        """
+        Serialize the current PRecord using custom serializer functions for fields where
+        such have been supplied.
+        """
+        return dict((k, serialize(self._precord_fields[k].serializer, format, v)) for k, v in self.items())
+
+
+class _PRecordEvolver(PMap._Evolver):
+    __slots__ = ('_destination_cls', '_invariant_error_codes', '_missing_fields', '_factory_fields', '_ignore_extra')
+
+    def __init__(self, cls, original_pmap, _factory_fields=None, _ignore_extra=False):
+        super(_PRecordEvolver, self).__init__(original_pmap)
+        self._destination_cls = cls
+        self._invariant_error_codes = []
+        self._missing_fields = []
+        self._factory_fields = _factory_fields
+        self._ignore_extra = _ignore_extra
+
+    def __setitem__(self, key, original_value):
+        self.set(key, original_value)
+
+    def set(self, key, original_value):
+        field = self._destination_cls._precord_fields.get(key)
+        if field:
+            if self._factory_fields is None or field in self._factory_fields:
+                try:
+                    if is_field_ignore_extra_complaint(PRecord, field, self._ignore_extra):
+                        value = field.factory(original_value, ignore_extra=self._ignore_extra)
+                    else:
+                        value = field.factory(original_value)
+                except InvariantException as e:
+                    self._invariant_error_codes += e.invariant_errors
+                    self._missing_fields += e.missing_fields
+                    return self
+            else:
+                value = original_value
+
+            check_type(self._destination_cls, field, key, value)
+
+            is_ok, error_code = field.invariant(value)
+            if not is_ok:
+                self._invariant_error_codes.append(error_code)
+
+            return super(_PRecordEvolver, self).set(key, value)
+        else:
+            raise AttributeError("'{0}' is not among the specified fields for {1}".format(key, self._destination_cls.__name__))
+
+    def persistent(self):
+        cls = self._destination_cls
+        is_dirty = self.is_dirty()
+        pm = super(_PRecordEvolver, self).persistent()
+        if is_dirty or not isinstance(pm, cls):
+            result = cls(_precord_buckets=pm._buckets, _precord_size=pm._size)
+        else:
+            result = pm
+
+        if cls._precord_mandatory_fields:
+            self._missing_fields += tuple('{0}.{1}'.format(cls.__name__, f) for f
+                                          in (cls._precord_mandatory_fields - set(result.keys())))
+
+        if self._invariant_error_codes or self._missing_fields:
+            raise InvariantException(tuple(self._invariant_error_codes), tuple(self._missing_fields),
+                                     'Field invariant failed')
+
+        check_global_invariants(result, cls._precord_invariants)
+
+        return result
diff --git a/third_party/python/pyrsistent/pyrsistent/_pset.py b/third_party/python/pyrsistent/pyrsistent/_pset.py
new file mode 100644
index 0000000000..a972ec533b
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pset.py
@@ -0,0 +1,229 @@
+from ._compat import Set, Hashable
+import sys
+from pyrsistent._pmap import pmap
+
+PY2 = sys.version_info[0] < 3
+
+
+class PSet(object):
+    """
+    Persistent set implementation. Built on top of the persistent map. The set supports all operations
+    in the Set protocol and is Hashable.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`s` or :py:func:`pset`
+    to create an instance.
+
+    Random access and insert is log32(n) where n is the size of the set.
+
+    Some examples:
+
+    >>> s = pset([1, 2, 3, 1])
+    >>> s2 = s.add(4)
+    >>> s3 = s2.remove(2)
+    >>> s
+    pset([1, 2, 3])
+    >>> s2
+    pset([1, 2, 3, 4])
+    >>> s3
+    pset([1, 3, 4])
+    """
+    __slots__ = ('_map', '__weakref__')
+
+    def __new__(cls, m):
+        self = super(PSet, cls).__new__(cls)
+        self._map = m
+        return self
+
+    def __contains__(self, element):
+        return element in self._map
+
+    def __iter__(self):
+        return iter(self._map)
+
+    def __len__(self):
+        return len(self._map)
+
+    def __repr__(self):
+        if PY2 or not self:
+            return 'p' + str(set(self))
+
+        return 'pset([{0}])'.format(str(set(self))[1:-1])
+
+    def __str__(self):
+        return self.__repr__()
+
+    def __hash__(self):
+        return hash(self._map)
+
+    def __reduce__(self):
+        # Pickling support
+        return pset, (list(self),)
+
+    @classmethod
+    def _from_iterable(cls, it, pre_size=8):
+        return PSet(pmap(dict((k, True) for k in it), pre_size=pre_size))
+
+    def add(self, element):
+        """
+        Return a new PSet with element added
+
+        >>> s1 = s(1, 2)
+        >>> s1.add(3)
+        pset([1, 2, 3])
+        """
+        return self.evolver().add(element).persistent()
+
+    def update(self, iterable):
+        """
+        Return a new PSet with elements in iterable added
+
+        >>> s1 = s(1, 2)
+        >>> s1.update([3, 4, 4])
+        pset([1, 2, 3, 4])
+        """
+        e = self.evolver()
+        for element in iterable:
+            e.add(element)
+
+        return e.persistent()
+
+    def remove(self, element):
+        """
+        Return a new PSet with element removed. Raises KeyError if element is not present.
+
+        >>> s1 = s(1, 2)
+        >>> s1.remove(2)
+        pset([1])
+        """
+        if element in self._map:
+            return self.evolver().remove(element).persistent()
+
+        raise KeyError("Element '%s' not present in PSet" % element)
+
+    def discard(self, element):
+        """
+        Return a new PSet with element removed. Returns itself if element is not present.
+        """
+        if element in self._map:
+            return self.evolver().remove(element).persistent()
+
+        return self
+
+    class _Evolver(object):
+        __slots__ = ('_original_pset', '_pmap_evolver')
+
+        def __init__(self, original_pset):
+            self._original_pset = original_pset
+            self._pmap_evolver = original_pset._map.evolver()
+
+        def add(self, element):
+            self._pmap_evolver[element] = True
+            return self
+
+        def remove(self, element):
+            del self._pmap_evolver[element]
+            return self
+
+        def is_dirty(self):
+            return self._pmap_evolver.is_dirty()
+
+        def persistent(self):
+            if not self.is_dirty():
+                return  self._original_pset
+
+            return PSet(self._pmap_evolver.persistent())
+
+        def __len__(self):
+            return len(self._pmap_evolver)
+
+    def copy(self):
+        return self
+
+    def evolver(self):
+        """
+        Create a new evolver for this pset. For a discussion on evolvers in general see the
+        documentation for the pvector evolver.
+
+        Create the evolver and perform various mutating updates to it:
+
+        >>> s1 = s(1, 2, 3)
+        >>> e = s1.evolver()
+        >>> _ = e.add(4)
+        >>> len(e)
+        4
+        >>> _ = e.remove(1)
+
+        The underlying pset remains the same:
+
+        >>> s1
+        pset([1, 2, 3])
+
+        The changes are kept in the evolver. An updated pmap can be created using the
+        persistent() function on the evolver.
+
+        >>> s2 = e.persistent()
+        >>> s2
+        pset([2, 3, 4])
+
+        The new pset will share data with the original pset in the same way that would have
+        been done if only using operations on the pset.
+        """
+        return PSet._Evolver(self)
+
+    # All the operations and comparisons you would expect on a set.
+    #
+    # This is not very beautiful. If we avoid inheriting from PSet we can use the
+    # __slots__ concepts (which requires a new style class) and hopefully save some memory.
+    __le__ = Set.__le__
+    __lt__ = Set.__lt__
+    __gt__ = Set.__gt__
+    __ge__ = Set.__ge__
+    __eq__ = Set.__eq__
+    __ne__ = Set.__ne__
+
+    __and__ = Set.__and__
+    __or__ = Set.__or__
+    __sub__ = Set.__sub__
+    __xor__ = Set.__xor__
+
+    issubset = __le__
+    issuperset = __ge__
+    union = __or__
+    intersection = __and__
+    difference = __sub__
+    symmetric_difference = __xor__
+
+    isdisjoint = Set.isdisjoint
+
+Set.register(PSet)
+Hashable.register(PSet)
+
+_EMPTY_PSET = PSet(pmap())
+
+
+def pset(iterable=(), pre_size=8):
+    """
+    Creates a persistent set from iterable. Optionally takes a sizing parameter equivalent to that
+    used for :py:func:`pmap`.
+
+    >>> s1 = pset([1, 2, 3, 2])
+    >>> s1
+    pset([1, 2, 3])
+    """
+    if not iterable:
+        return _EMPTY_PSET
+
+    return PSet._from_iterable(iterable, pre_size=pre_size)
+
+
+def s(*elements):
+    """
+    Create a persistent set.
+
+    Takes an arbitrary number of arguments to insert into the new set.
+
+    >>> s1 = s(1, 2, 3, 2)
+    >>> s1
+    pset([1, 2, 3])
+    """
+    return pset(elements)
diff --git a/third_party/python/pyrsistent/pyrsistent/_pvector.py b/third_party/python/pyrsistent/pyrsistent/_pvector.py
new file mode 100644
index 0000000000..82232782b7
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_pvector.py
@@ -0,0 +1,713 @@
+from abc import abstractmethod, ABCMeta
+from ._compat import Sequence, Hashable
+from numbers import Integral
+import operator
+import six
+from pyrsistent._transformations import transform
+
+
+def _bitcount(val):
+    return bin(val).count("1")
+
+BRANCH_FACTOR = 32
+BIT_MASK = BRANCH_FACTOR - 1
+SHIFT = _bitcount(BIT_MASK)
+
+
+def compare_pvector(v, other, operator):
+    return operator(v.tolist(), other.tolist() if isinstance(other, PVector) else other)
+
+
+def _index_or_slice(index, stop):
+    if stop is None:
+        return index
+
+    return slice(index, stop)
+
+
+class PythonPVector(object):
+    """
+    Support structure for PVector that implements structural sharing for vectors using a trie.
+    """
+    __slots__ = ('_count', '_shift', '_root', '_tail', '_tail_offset', '__weakref__')
+
+    def __new__(cls, count, shift, root, tail):
+        self = super(PythonPVector, cls).__new__(cls)
+        self._count = count
+        self._shift = shift
+        self._root = root
+        self._tail = tail
+
+        # Derived attribute stored for performance
+        self._tail_offset = self._count - len(self._tail)
+        return self
+
+    def __len__(self):
+        return self._count
+
+    def __getitem__(self, index):
+        if isinstance(index, slice):
+            # There are more conditions than the below where it would be OK to
+            # return ourselves, implement those...
+            if index.start is None and index.stop is None and index.step is None:
+                return self
+
+            # This is a bit nasty realizing the whole structure as a list before
+            # slicing it but it is the fastest way I've found to date, and it's easy :-)
+            return _EMPTY_PVECTOR.extend(self.tolist()[index])
+
+        if index < 0:
+            index += self._count
+
+        return PythonPVector._node_for(self, index)[index & BIT_MASK]
+
+    def __add__(self, other):
+        return self.extend(other)
+
+    def __repr__(self):
+        return 'pvector({0})'.format(str(self.tolist()))
+
+    def __str__(self):
+        return self.__repr__()
+
+    def __iter__(self):
+        # This is kind of lazy and will produce some memory overhead but it is the fasted method
+        # by far of those tried since it uses the speed of the built in python list directly.
+        return iter(self.tolist())
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __eq__(self, other):
+        return self is other or (hasattr(other, '__len__') and self._count == len(other)) and compare_pvector(self, other, operator.eq)
+
+    def __gt__(self, other):
+        return compare_pvector(self, other, operator.gt)
+
+    def __lt__(self, other):
+        return compare_pvector(self, other, operator.lt)
+
+    def __ge__(self, other):
+        return compare_pvector(self, other, operator.ge)
+
+    def __le__(self, other):
+        return compare_pvector(self, other, operator.le)
+
+    def __mul__(self, times):
+        if times <= 0 or self is _EMPTY_PVECTOR:
+            return _EMPTY_PVECTOR
+
+        if times == 1:
+            return self
+
+        return _EMPTY_PVECTOR.extend(times * self.tolist())
+
+    __rmul__ = __mul__
+
+    def _fill_list(self, node, shift, the_list):
+        if shift:
+            shift -= SHIFT
+            for n in node:
+                self._fill_list(n, shift, the_list)
+        else:
+            the_list.extend(node)
+
+    def tolist(self):
+        """
+        The fastest way to convert the vector into a python list.
+        """
+        the_list = []
+        self._fill_list(self._root, self._shift, the_list)
+        the_list.extend(self._tail)
+        return the_list
+
+    def _totuple(self):
+        """
+        Returns the content as a python tuple.
+        """
+        return tuple(self.tolist())
+
+    def __hash__(self):
+        # Taking the easy way out again...
+        return hash(self._totuple())
+
+    def transform(self, *transformations):
+        return transform(self, transformations)
+
+    def __reduce__(self):
+        # Pickling support
+        return pvector, (self.tolist(),)
+
+    def mset(self, *args):
+        if len(args) % 2:
+            raise TypeError("mset expected an even number of arguments")
+
+        evolver = self.evolver()
+        for i in range(0, len(args), 2):
+            evolver[args[i]] = args[i+1]
+
+        return evolver.persistent()
+
+    class Evolver(object):
+        __slots__ = ('_count', '_shift', '_root', '_tail', '_tail_offset', '_dirty_nodes',
+                     '_extra_tail', '_cached_leafs', '_orig_pvector')
+
+        def __init__(self, v):
+            self._reset(v)
+
+        def __getitem__(self, index):
+            if not isinstance(index, Integral):
+                raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__)
+
+            if index < 0:
+                index += self._count + len(self._extra_tail)
+
+            if self._count <= index < self._count + len(self._extra_tail):
+                return self._extra_tail[index - self._count]
+
+            return PythonPVector._node_for(self, index)[index & BIT_MASK]
+
+        def _reset(self, v):
+            self._count = v._count
+            self._shift = v._shift
+            self._root = v._root
+            self._tail = v._tail
+            self._tail_offset = v._tail_offset
+            self._dirty_nodes = {}
+            self._cached_leafs = {}
+            self._extra_tail = []
+            self._orig_pvector = v
+
+        def append(self, element):
+            self._extra_tail.append(element)
+            return self
+
+        def extend(self, iterable):
+            self._extra_tail.extend(iterable)
+            return self
+
+        def set(self, index, val):
+            self[index] = val
+            return self
+
+        def __setitem__(self, index, val):
+            if not isinstance(index, Integral):
+                raise TypeError("'%s' object cannot be interpreted as an index" % type(index).__name__)
+
+            if index < 0:
+                index += self._count + len(self._extra_tail)
+
+            if 0 <= index < self._count:
+                node = self._cached_leafs.get(index >> SHIFT)
+                if node:
+                    node[index & BIT_MASK] = val
+                elif index >= self._tail_offset:
+                    if id(self._tail) not in self._dirty_nodes:
+                        self._tail = list(self._tail)
+                        self._dirty_nodes[id(self._tail)] = True
+                        self._cached_leafs[index >> SHIFT] = self._tail
+                    self._tail[index & BIT_MASK] = val
+                else:
+                    self._root = self._do_set(self._shift, self._root, index, val)
+            elif self._count <= index < self._count + len(self._extra_tail):
+                self._extra_tail[index - self._count] = val
+            elif index == self._count + len(self._extra_tail):
+                self._extra_tail.append(val)
+            else:
+                raise IndexError("Index out of range: %s" % (index,))
+
+        def _do_set(self, level, node, i, val):
+            if id(node) in self._dirty_nodes:
+                ret = node
+            else:
+                ret = list(node)
+                self._dirty_nodes[id(ret)] = True
+
+            if level == 0:
+                ret[i & BIT_MASK] = val
+                self._cached_leafs[i >> SHIFT] = ret
+            else:
+                sub_index = (i >> level) & BIT_MASK  # >>>
+                ret[sub_index] = self._do_set(level - SHIFT, node[sub_index], i, val)
+
+            return ret
+
+        def delete(self, index):
+            del self[index]
+            return self
+
+        def __delitem__(self, key):
+            if self._orig_pvector:
+                # All structural sharing bets are off, base evolver on _extra_tail only
+                l = PythonPVector(self._count, self._shift, self._root, self._tail).tolist()
+                l.extend(self._extra_tail)
+                self._reset(_EMPTY_PVECTOR)
+                self._extra_tail = l
+
+            del self._extra_tail[key]
+
+        def persistent(self):
+            result = self._orig_pvector
+            if self.is_dirty():
+                result = PythonPVector(self._count, self._shift, self._root, self._tail).extend(self._extra_tail)
+                self._reset(result)
+
+            return result
+
+        def __len__(self):
+            return self._count + len(self._extra_tail)
+
+        def is_dirty(self):
+            return bool(self._dirty_nodes or self._extra_tail)
+
+    def evolver(self):
+        return PythonPVector.Evolver(self)
+
+    def set(self, i, val):
+        # This method could be implemented by a call to mset() but doing so would cause
+        # a ~5 X performance penalty on PyPy (considered the primary platform for this implementation
+        #  of PVector) so we're keeping this implementation for now.
+
+        if not isinstance(i, Integral):
+            raise TypeError("'%s' object cannot be interpreted as an index" % type(i).__name__)
+
+        if i < 0:
+            i += self._count
+
+        if 0 <= i < self._count:
+            if i >= self._tail_offset:
+                new_tail = list(self._tail)
+                new_tail[i & BIT_MASK] = val
+                return PythonPVector(self._count, self._shift, self._root, new_tail)
+
+            return PythonPVector(self._count, self._shift, self._do_set(self._shift, self._root, i, val), self._tail)
+
+        if i == self._count:
+            return self.append(val)
+
+        raise IndexError("Index out of range: %s" % (i,))
+
+    def _do_set(self, level, node, i, val):
+        ret = list(node)
+        if level == 0:
+            ret[i & BIT_MASK] = val
+        else:
+            sub_index = (i >> level) & BIT_MASK  # >>>
+            ret[sub_index] = self._do_set(level - SHIFT, node[sub_index], i, val)
+
+        return ret
+
+    @staticmethod
+    def _node_for(pvector_like, i):
+        if 0 <= i < pvector_like._count:
+            if i >= pvector_like._tail_offset:
+                return pvector_like._tail
+
+            node = pvector_like._root
+            for level in range(pvector_like._shift, 0, -SHIFT):
+                node = node[(i >> level) & BIT_MASK]  # >>>
+
+            return node
+
+        raise IndexError("Index out of range: %s" % (i,))
+
+    def _create_new_root(self):
+        new_shift = self._shift
+
+        # Overflow root?
+        if (self._count >> SHIFT) > (1 << self._shift): # >>>
+            new_root = [self._root, self._new_path(self._shift, self._tail)]
+            new_shift += SHIFT
+        else:
+            new_root = self._push_tail(self._shift, self._root, self._tail)
+
+        return new_root, new_shift
+
+    def append(self, val):
+        if len(self._tail) < BRANCH_FACTOR:
+            new_tail = list(self._tail)
+            new_tail.append(val)
+            return PythonPVector(self._count + 1, self._shift, self._root, new_tail)
+
+        # Full tail, push into tree
+        new_root, new_shift = self._create_new_root()
+        return PythonPVector(self._count + 1, new_shift, new_root, [val])
+
+    def _new_path(self, level, node):
+        if level == 0:
+            return node
+
+        return [self._new_path(level - SHIFT, node)]
+
+    def _mutating_insert_tail(self):
+        self._root, self._shift = self._create_new_root()
+        self._tail = []
+
+    def _mutating_fill_tail(self, offset, sequence):
+        max_delta_len = BRANCH_FACTOR - len(self._tail)
+        delta = sequence[offset:offset + max_delta_len]
+        self._tail.extend(delta)
+        delta_len = len(delta)
+        self._count += delta_len
+        return offset + delta_len
+
+    def _mutating_extend(self, sequence):
+        offset = 0
+        sequence_len = len(sequence)
+        while offset < sequence_len:
+            offset = self._mutating_fill_tail(offset, sequence)
+            if len(self._tail) == BRANCH_FACTOR:
+                self._mutating_insert_tail()
+
+        self._tail_offset = self._count - len(self._tail)
+
+    def extend(self, obj):
+        # Mutates the new vector directly for efficiency but that's only an
+        # implementation detail, once it is returned it should be considered immutable
+        l = obj.tolist() if isinstance(obj, PythonPVector) else list(obj)
+        if l:
+            new_vector = self.append(l[0])
+            new_vector._mutating_extend(l[1:])
+            return new_vector
+
+        return self
+
+    def _push_tail(self, level, parent, tail_node):
+        """
+        if parent is leaf, insert node,
+        else does it map to an existing child? ->
+             node_to_insert = push node one more level
+        else alloc new path
+
+        return  node_to_insert placed in copy of parent
+        """
+        ret = list(parent)
+
+        if level == SHIFT:
+            ret.append(tail_node)
+            return ret
+
+        sub_index = ((self._count - 1) >> level) & BIT_MASK  # >>>
+        if len(parent) > sub_index:
+            ret[sub_index] = self._push_tail(level - SHIFT, parent[sub_index], tail_node)
+            return ret
+
+        ret.append(self._new_path(level - SHIFT, tail_node))
+        return ret
+
+    def index(self, value, *args, **kwargs):
+        return self.tolist().index(value, *args, **kwargs)
+
+    def count(self, value):
+        return self.tolist().count(value)
+
+    def delete(self, index, stop=None):
+        l = self.tolist()
+        del l[_index_or_slice(index, stop)]
+        return _EMPTY_PVECTOR.extend(l)
+
+    def remove(self, value):
+        l = self.tolist()
+        l.remove(value)
+        return _EMPTY_PVECTOR.extend(l)
+
+@six.add_metaclass(ABCMeta)
+class PVector(object):
+    """
+    Persistent vector implementation. Meant as a replacement for the cases where you would normally
+    use a Python list.
+
+    Do not instantiate directly, instead use the factory functions :py:func:`v` and :py:func:`pvector` to
+    create an instance.
+
+    Heavily influenced by the persistent vector available in Clojure. Initially this was more or
+    less just a port of the Java code for the Clojure vector. It has since been modified and to
+    some extent optimized for usage in Python.
+
+    The vector is organized as a trie, any mutating method will return a new vector that contains the changes. No
+    updates are done to the original vector. Structural sharing between vectors are applied where possible to save
+    space and to avoid making complete copies.
+
+    This structure corresponds most closely to the built in list type and is intended as a replacement. Where the
+    semantics are the same (more or less) the same function names have been used but for some cases it is not possible,
+    for example assignments.
+
+    The PVector implements the Sequence protocol and is Hashable.
+
+    Inserts are amortized O(1). Random access is log32(n) where n is the size of the vector.
+
+    The following are examples of some common operations on persistent vectors:
+
+    >>> p = v(1, 2, 3)
+    >>> p2 = p.append(4)
+    >>> p3 = p2.extend([5, 6, 7])
+    >>> p
+    pvector([1, 2, 3])
+    >>> p2
+    pvector([1, 2, 3, 4])
+    >>> p3
+    pvector([1, 2, 3, 4, 5, 6, 7])
+    >>> p3[5]
+    6
+    >>> p.set(1, 99)
+    pvector([1, 99, 3])
+    >>>
+    """
+
+    @abstractmethod
+    def __len__(self):
+        """
+        >>> len(v(1, 2, 3))
+        3
+        """
+
+    @abstractmethod
+    def __getitem__(self, index):
+        """
+        Get value at index. Full slicing support.
+
+        >>> v1 = v(5, 6, 7, 8)
+        >>> v1[2]
+        7
+        >>> v1[1:3]
+        pvector([6, 7])
+        """
+
+    @abstractmethod
+    def __add__(self, other):
+        """
+        >>> v1 = v(1, 2)
+        >>> v2 = v(3, 4)
+        >>> v1 + v2
+        pvector([1, 2, 3, 4])
+        """
+
+    @abstractmethod
+    def __mul__(self, times):
+        """
+        >>> v1 = v(1, 2)
+        >>> 3 * v1
+        pvector([1, 2, 1, 2, 1, 2])
+        """
+
+    @abstractmethod
+    def __hash__(self):
+        """
+        >>> v1 = v(1, 2, 3)
+        >>> v2 = v(1, 2, 3)
+        >>> hash(v1) == hash(v2)
+        True
+        """
+
+    @abstractmethod
+    def evolver(self):
+        """
+        Create a new evolver for this pvector. The evolver acts as a mutable view of the vector
+        with "transaction like" semantics. No part of the underlying vector i updated, it is still
+        fully immutable. Furthermore multiple evolvers created from the same pvector do not
+        interfere with each other.
+
+        You may want to use an evolver instead of working directly with the pvector in the
+        following cases:
+
+        * Multiple updates are done to the same vector and the intermediate results are of no
+          interest. In this case using an evolver may be a more efficient and easier to work with.
+        * You need to pass a vector into a legacy function or a function that you have no control
+          over which performs in place mutations of lists. In this case pass an evolver instance
+          instead and then create a new pvector from the evolver once the function returns.
+
+        The following example illustrates a typical workflow when working with evolvers. It also
+        displays most of the API (which i kept small by design, you should not be tempted to
+        use evolvers in excess ;-)).
+
+        Create the evolver and perform various mutating updates to it:
+
+        >>> v1 = v(1, 2, 3, 4, 5)
+        >>> e = v1.evolver()
+        >>> e[1] = 22
+        >>> _ = e.append(6)
+        >>> _ = e.extend([7, 8, 9])
+        >>> e[8] += 1
+        >>> len(e)
+        9
+
+        The underlying pvector remains the same:
+
+        >>> v1
+        pvector([1, 2, 3, 4, 5])
+
+        The changes are kept in the evolver. An updated pvector can be created using the
+        persistent() function on the evolver.
+
+        >>> v2 = e.persistent()
+        >>> v2
+        pvector([1, 22, 3, 4, 5, 6, 7, 8, 10])
+
+        The new pvector will share data with the original pvector in the same way that would have
+        been done if only using operations on the pvector.
+        """
+
+    @abstractmethod
+    def mset(self, *args):
+        """
+        Return a new vector with elements in specified positions replaced by values (multi set).
+
+        Elements on even positions in the argument list are interpreted as indexes while
+        elements on odd positions are considered values.
+
+        >>> v1 = v(1, 2, 3)
+        >>> v1.mset(0, 11, 2, 33)
+        pvector([11, 2, 33])
+        """
+
+    @abstractmethod
+    def set(self, i, val):
+        """
+        Return a new vector with element at position i replaced with val. The original vector remains unchanged.
+
+        Setting a value one step beyond the end of the vector is equal to appending. Setting beyond that will
+        result in an IndexError.
+
+        >>> v1 = v(1, 2, 3)
+        >>> v1.set(1, 4)
+        pvector([1, 4, 3])
+        >>> v1.set(3, 4)
+        pvector([1, 2, 3, 4])
+        >>> v1.set(-1, 4)
+        pvector([1, 2, 4])
+        """
+
+    @abstractmethod
+    def append(self, val):
+        """
+        Return a new vector with val appended.
+
+        >>> v1 = v(1, 2)
+        >>> v1.append(3)
+        pvector([1, 2, 3])
+        """
+
+    @abstractmethod
+    def extend(self, obj):
+        """
+        Return a new vector with all values in obj appended to it. Obj may be another
+        PVector or any other Iterable.
+
+        >>> v1 = v(1, 2, 3)
+        >>> v1.extend([4, 5])
+        pvector([1, 2, 3, 4, 5])
+        """
+
+    @abstractmethod
+    def index(self, value, *args, **kwargs):
+        """
+        Return first index of value. Additional indexes may be supplied to limit the search to a
+        sub range of the vector.
+
+        >>> v1 = v(1, 2, 3, 4, 3)
+        >>> v1.index(3)
+        2
+        >>> v1.index(3, 3, 5)
+        4
+        """
+
+    @abstractmethod
+    def count(self, value):
+        """
+        Return the number of times that value appears in the vector.
+
+        >>> v1 = v(1, 4, 3, 4)
+        >>> v1.count(4)
+        2
+        """
+
+    @abstractmethod
+    def transform(self, *transformations):
+        """
+        Transform arbitrarily complex combinations of PVectors and PMaps. A transformation
+        consists of two parts. One match expression that specifies which elements to transform
+        and one transformation function that performs the actual transformation.
+
+        >>> from pyrsistent import freeze, ny
+        >>> news_paper = freeze({'articles': [{'author': 'Sara', 'content': 'A short article'},
+        ...                                   {'author': 'Steve', 'content': 'A slightly longer article'}],
+        ...                      'weather': {'temperature': '11C', 'wind': '5m/s'}})
+        >>> short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:25] + '...' if len(c) > 25 else c)
+        >>> very_short_news = news_paper.transform(['articles', ny, 'content'], lambda c: c[:15] + '...' if len(c) > 15 else c)
+        >>> very_short_news.articles[0].content
+        'A short article'
+        >>> very_short_news.articles[1].content
+        'A slightly long...'
+
+        When nothing has been transformed the original data structure is kept
+
+        >>> short_news is news_paper
+        True
+        >>> very_short_news is news_paper
+        False
+        >>> very_short_news.articles[0] is news_paper.articles[0]
+        True
+        """
+
+    @abstractmethod
+    def delete(self, index, stop=None):
+        """
+        Delete a portion of the vector by index or range.
+
+        >>> v1 = v(1, 2, 3, 4, 5)
+        >>> v1.delete(1)
+        pvector([1, 3, 4, 5])
+        >>> v1.delete(1, 3)
+        pvector([1, 4, 5])
+        """
+
+    @abstractmethod
+    def remove(self, value):
+        """
+        Remove the first occurrence of a value from the vector.
+
+        >>> v1 = v(1, 2, 3, 2, 1)
+        >>> v2 = v1.remove(1)
+        >>> v2
+        pvector([2, 3, 2, 1])
+        >>> v2.remove(1)
+        pvector([2, 3, 2])
+        """
+
+
+_EMPTY_PVECTOR = PythonPVector(0, SHIFT, [], [])
+PVector.register(PythonPVector)
+Sequence.register(PVector)
+Hashable.register(PVector)
+
+def python_pvector(iterable=()):
+    """
+    Create a new persistent vector containing the elements in iterable.
+
+    >>> v1 = pvector([1, 2, 3])
+    >>> v1
+    pvector([1, 2, 3])
+    """
+    return _EMPTY_PVECTOR.extend(iterable)
+
+try:
+    # Use the C extension as underlying trie implementation if it is available
+    import os
+    if os.environ.get('PYRSISTENT_NO_C_EXTENSION'):
+        pvector = python_pvector
+    else:
+        from pvectorc import pvector
+        PVector.register(type(pvector()))
+except ImportError:
+    pvector = python_pvector
+
+
+def v(*elements):
+    """
+    Create a new persistent vector containing all parameters to this function.
+
+    >>> v1 = v(1, 2, 3)
+    >>> v1
+    pvector([1, 2, 3])
+    """
+    return pvector(elements)
diff --git a/third_party/python/pyrsistent/pyrsistent/_toolz.py b/third_party/python/pyrsistent/pyrsistent/_toolz.py
new file mode 100644
index 0000000000..6643ee860d
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_toolz.py
@@ -0,0 +1,83 @@
+"""
+Functionality copied from the toolz package to avoid having
+to add toolz as a dependency.
+
+See https://github.com/pytoolz/toolz/.
+
+toolz is relased under BSD licence. Below is the licence text
+from toolz as it appeared when copying the code.
+
+--------------------------------------------------------------
+
+Copyright (c) 2013 Matthew Rocklin
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+  a. Redistributions of source code must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+  b. Redistributions in binary form must reproduce the above copyright
+     notice, this list of conditions and the following disclaimer in the
+     documentation and/or other materials provided with the distribution.
+  c. Neither the name of toolz nor the names of its contributors
+     may be used to endorse or promote products derived from this software
+     without specific prior written permission.
+
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
+DAMAGE.
+"""
+import operator
+from six.moves import reduce
+
+
+def get_in(keys, coll, default=None, no_default=False):
+    """
+    NB: This is a straight copy of the get_in implementation found in
+        the toolz library (https://github.com/pytoolz/toolz/). It works
+        with persistent data structures as well as the corresponding
+        datastructures from the stdlib.
+
+    Returns coll[i0][i1]...[iX] where [i0, i1, ..., iX]==keys.
+
+    If coll[i0][i1]...[iX] cannot be found, returns ``default``, unless
+    ``no_default`` is specified, then it raises KeyError or IndexError.
+
+    ``get_in`` is a generalization of ``operator.getitem`` for nested data
+    structures such as dictionaries and lists.
+    >>> from pyrsistent import freeze
+    >>> transaction = freeze({'name': 'Alice',
+    ...                       'purchase': {'items': ['Apple', 'Orange'],
+    ...                                    'costs': [0.50, 1.25]},
+    ...                       'credit card': '5555-1234-1234-1234'})
+    >>> get_in(['purchase', 'items', 0], transaction)
+    'Apple'
+    >>> get_in(['name'], transaction)
+    'Alice'
+    >>> get_in(['purchase', 'total'], transaction)
+    >>> get_in(['purchase', 'items', 'apple'], transaction)
+    >>> get_in(['purchase', 'items', 10], transaction)
+    >>> get_in(['purchase', 'total'], transaction, 0)
+    0
+    >>> get_in(['y'], {}, no_default=True)
+    Traceback (most recent call last):
+        ...
+    KeyError: 'y'
+    """
+    try:
+        return reduce(operator.getitem, keys, coll)
+    except (KeyError, IndexError, TypeError):
+        if no_default:
+            raise
+        return default
\ No newline at end of file
diff --git a/third_party/python/pyrsistent/pyrsistent/_transformations.py b/third_party/python/pyrsistent/pyrsistent/_transformations.py
new file mode 100644
index 0000000000..612098969b
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/_transformations.py
@@ -0,0 +1,143 @@
+import re
+import six
+try:
+    from inspect import Parameter, signature
+except ImportError:
+    signature = None
+    try:
+        from inspect import getfullargspec as getargspec
+    except ImportError:
+        from inspect import getargspec
+
+
+_EMPTY_SENTINEL = object()
+
+
+def inc(x):
+    """ Add one to the current value """
+    return x + 1
+
+
+def dec(x):
+    """ Subtract one from the current value """
+    return x - 1
+
+
+def discard(evolver, key):
+    """ Discard the element and returns a structure without the discarded elements """
+    try:
+        del evolver[key]
+    except KeyError:
+        pass
+
+
+# Matchers
+def rex(expr):
+    """ Regular expression matcher to use together with transform functions """
+    r = re.compile(expr)
+    return lambda key: isinstance(key, six.string_types) and r.match(key)
+
+
+def ny(_):
+    """ Matcher that matches any value """
+    return True
+
+
+# Support functions
+def _chunks(l, n):
+    for i in range(0, len(l), n):
+        yield l[i:i + n]
+
+
+def transform(structure, transformations):
+    r = structure
+    for path, command in _chunks(transformations, 2):
+        r = _do_to_path(r, path, command)
+    return r
+
+
+def _do_to_path(structure, path, command):
+    if not path:
+        return command(structure) if callable(command) else command
+
+    kvs = _get_keys_and_values(structure, path[0])
+    return _update_structure(structure, kvs, path[1:], command)
+
+
+def _items(structure):
+    try:
+        return structure.items()
+    except AttributeError:
+        # Support wider range of structures by adding a transform_items() or similar?
+        return list(enumerate(structure))
+
+
+def _get(structure, key, default):
+    try:
+        if hasattr(structure, '__getitem__'):
+            return structure[key]
+
+        return getattr(structure, key)
+
+    except (IndexError, KeyError):
+        return default
+
+
+def _get_keys_and_values(structure, key_spec):
+    if callable(key_spec):
+        # Support predicates as callable objects in the path
+        arity = _get_arity(key_spec)
+        if arity == 1:
+            # Unary predicates are called with the "key" of the path
+            # - eg a key in a mapping, an index in a sequence.
+            return [(k, v) for k, v in _items(structure) if key_spec(k)]
+        elif arity == 2:
+            # Binary predicates are called with the key and the corresponding
+            # value.
+            return [(k, v) for k, v in _items(structure) if key_spec(k, v)]
+        else:
+            # Other arities are an error.
+            raise ValueError(
+                "callable in transform path must take 1 or 2 arguments"
+            )
+
+    # Non-callables are used as-is as a key.
+    return [(key_spec, _get(structure, key_spec, _EMPTY_SENTINEL))]
+
+
+if signature is None:
+    def _get_arity(f):
+        argspec = getargspec(f)
+        return len(argspec.args) - len(argspec.defaults or ())
+else:
+    def _get_arity(f):
+        return sum(
+            1
+            for p
+            in signature(f).parameters.values()
+            if p.default is Parameter.empty
+            and p.kind in (Parameter.POSITIONAL_ONLY, Parameter.POSITIONAL_OR_KEYWORD)
+        )
+
+
+def _update_structure(structure, kvs, path, command):
+    from pyrsistent._pmap import pmap
+    e = structure.evolver()
+    if not path and command is discard:
+        # Do this in reverse to avoid index problems with vectors. See #92.
+        for k, v in reversed(kvs):
+            discard(e, k)
+    else:
+        for k, v in kvs:
+            is_empty = False
+            if v is _EMPTY_SENTINEL:
+                # Allow expansion of structure but make sure to cover the case
+                # when an empty pmap is added as leaf node. See #154.
+                is_empty = True
+                v = pmap()
+
+            result = _do_to_path(v, path, command)
+            if result is not v or is_empty:
+                e[k] = result
+
+    return e.persistent()
diff --git a/third_party/python/pyrsistent/pyrsistent/py.typed b/third_party/python/pyrsistent/pyrsistent/py.typed
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/py.typed
diff --git a/third_party/python/pyrsistent/pyrsistent/typing.py b/third_party/python/pyrsistent/pyrsistent/typing.py
new file mode 100644
index 0000000000..6a86c831ba
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/typing.py
@@ -0,0 +1,80 @@
+"""Helpers for use with type annotation.
+
+Use the empty classes in this module when annotating the types of Pyrsistent
+objects, instead of using the actual collection class.
+
+For example,
+
+    from pyrsistent import pvector
+    from pyrsistent.typing import PVector
+
+    myvector: PVector[str] = pvector(['a', 'b', 'c'])
+
+"""
+from __future__ import absolute_import
+
+try:
+    from typing import Container
+    from typing import Hashable
+    from typing import Generic
+    from typing import Iterable
+    from typing import Mapping
+    from typing import Sequence
+    from typing import Sized
+    from typing import TypeVar
+
+    __all__ = [
+        'CheckedPMap',
+        'CheckedPSet',
+        'CheckedPVector',
+        'PBag',
+        'PDeque',
+        'PList',
+        'PMap',
+        'PSet',
+        'PVector',
+    ]
+
+    T = TypeVar('T')
+    KT = TypeVar('KT')
+    VT = TypeVar('VT')
+
+    class CheckedPMap(Mapping[KT, VT], Hashable):
+        pass
+
+    # PSet.add and PSet.discard have different type signatures than that of Set.
+    class CheckedPSet(Generic[T], Hashable):
+        pass
+
+    class CheckedPVector(Sequence[T], Hashable):
+        pass
+
+    class PBag(Container[T], Iterable[T], Sized, Hashable):
+        pass
+
+    class PDeque(Sequence[T], Hashable):
+        pass
+
+    class PList(Sequence[T], Hashable):
+        pass
+
+    class PMap(Mapping[KT, VT], Hashable):
+        pass
+
+    # PSet.add and PSet.discard have different type signatures than that of Set.
+    class PSet(Generic[T], Hashable):
+        pass
+
+    class PVector(Sequence[T], Hashable):
+        pass
+
+    class PVectorEvolver(Generic[T]):
+        pass
+
+    class PMapEvolver(Generic[KT, VT]):
+        pass
+
+    class PSetEvolver(Generic[T]):
+        pass
+except ImportError:
+    pass
diff --git a/third_party/python/pyrsistent/pyrsistent/typing.pyi b/third_party/python/pyrsistent/pyrsistent/typing.pyi
new file mode 100644
index 0000000000..0221c48cc9
--- /dev/null
+++ b/third_party/python/pyrsistent/pyrsistent/typing.pyi
@@ -0,0 +1,292 @@
+# flake8: noqa: E704
+# from https://gist.github.com/WuTheFWasThat/091a17d4b5cab597dfd5d4c2d96faf09
+# Stubs for pyrsistent (Python 3.6)
+#
+from typing import Any
+from typing import Callable
+from typing import Dict
+from typing import Generic
+from typing import Hashable
+from typing import Iterator
+from typing import Iterable
+from typing import List
+from typing import Mapping
+from typing import Optional
+from typing import Sequence
+from typing import AbstractSet
+from typing import Sized
+from typing import Set
+from typing import Tuple
+from typing import TypeVar
+from typing import Type
+from typing import Union
+from typing import overload
+
+T = TypeVar('T')
+KT = TypeVar('KT')
+VT = TypeVar('VT')
+
+
+class PMap(Mapping[KT, VT], Hashable):
+    def __add__(self, other: PMap[KT, VT]) -> PMap[KT, VT]: ...
+    def __getitem__(self, key: KT) -> VT: ...
+    def __getattr__(self, key: str) -> VT: ...
+    def __hash__(self) -> int: ...
+    def __iter__(self) -> Iterator[KT]: ...
+    def __len__(self) -> int: ...
+    def copy(self) -> PMap[KT, VT]: ...
+    def discard(self, key: KT) -> PMap[KT, VT]: ...
+    def evolver(self) -> PMapEvolver[KT, VT]: ...
+    def iteritems(self) -> Iterable[Tuple[KT, VT]]: ...
+    def iterkeys(self) -> Iterable[KT]: ...
+    def itervalues(self) -> Iterable[VT]: ...
+    def remove(self, key: KT) -> PMap[KT, VT]: ...
+    def set(self, key: KT, val: VT) -> PMap[KT, VT]: ...
+    def transform(self, *transformations: Any) -> PMap[KT, VT]: ...
+    def update(self, *args: Mapping): ...
+    def update_with(self, update_fn: Callable[[VT, VT], VT], *args: Mapping) -> Any: ...
+
+
+class PMapEvolver(Generic[KT, VT]):
+    def __delitem__(self, key: KT) -> None: ...
+    def __getitem__(self, key: KT) -> VT: ...
+    def __len__(self) -> int: ...
+    def __setitem__(self, key: KT, val: VT) -> None: ...
+    def is_dirty(self) -> bool: ...
+    def persistent(self) -> PMap[KT, VT]: ...
+    def remove(self, key: KT) -> PMapEvolver[KT, VT]: ...
+    def set(self, key: KT, val: VT) -> PMapEvolver[KT, VT]: ...
+
+
+class PVector(Sequence[T], Hashable):
+    def __add__(self, other: PVector[T]) -> PVector[T]: ...
+    @overload
+    def __getitem__(self, index: int) -> T: ...
+    @overload
+    def __getitem__(self, index: slice) -> PVector[T]: ...
+    def __hash__(self) -> int: ...
+    def __len__(self) -> int: ...
+    def __mul__(self, other: PVector[T]) -> PVector[T]: ...
+    def append(self, val: T) -> PVector[T]: ...
+    def delete(self, index: int, stop: Optional[int]) -> PVector[T]: ...
+    def evolver(self) -> PVectorEvolver[T]: ...
+    def extend(self, obj: Iterable[T]) -> PVector[T]: ...
+    def tolist(self) -> List[T]: ...
+    def mset(self, *args: Iterable[Union[T, int]]) -> PVector[T]: ...
+    def remove(self, value: T) -> PVector[T]: ...
+    # Not compatible with MutableSequence
+    def set(self, i: int, val: T) -> PVector[T]: ...
+    def transform(self, *transformations: Any) -> PVector[T]: ...
+
+
+class PVectorEvolver(Sequence[T], Sized):
+    def __delitem__(self, i: Union[int, slice]) -> None: ...
+    @overload
+    def __getitem__(self, index: int) -> T: ...
+    # Not actually supported
+    @overload
+    def __getitem__(self, index: slice) -> PVectorEvolver[T]: ...
+    def __len__(self) -> int: ...
+    def __setitem__(self, index: int, val: T) -> None: ...
+    def append(self, val: T) -> PVectorEvolver[T]: ...
+    def delete(self, value: T) -> PVectorEvolver[T]: ...
+    def extend(self, obj: Iterable[T]) -> PVectorEvolver[T]: ...
+    def is_dirty(self) -> bool: ...
+    def persistent(self) -> PVector[T]: ...
+    def set(self, i: int, val: T) -> PVectorEvolver[T]: ...
+
+
+class PSet(AbstractSet[T], Hashable):
+    def __contains__(self, element: object) -> bool: ...
+    def __hash__(self) -> int: ...
+    def __iter__(self) -> Iterator[T]: ...
+    def __len__(self) -> int: ...
+    def add(self, element: T) -> PSet[T]: ...
+    def copy(self) -> PSet[T]: ...
+    def difference(self, iterable: Iterable) -> PSet[T]: ...
+    def discard(self, element: T) -> PSet[T]: ...
+    def evolver(self) -> PSetEvolver[T]: ...
+    def intersection(self, iterable: Iterable) -> PSet[T]: ...
+    def issubset(self, iterable: Iterable) -> bool: ...
+    def issuperset(self, iterable: Iterable) -> bool: ...
+    def remove(self, element: T) -> PSet[T]: ...
+    def symmetric_difference(self, iterable: Iterable[T]) -> PSet[T]: ...
+    def union(self, iterable: Iterable[T]) -> PSet[T]: ...
+    def update(self, iterable: Iterable[T]) -> PSet[T]: ...
+
+
+class PSetEvolver(Generic[T], Sized):
+    def __len__(self) -> int: ...
+    def add(self, element: T) -> PSetEvolver[T]: ...
+    def is_dirty(self) -> bool: ...
+    def persistent(self) -> PSet[T]: ...
+    def remove(self, element: T) -> PSetEvolver[T]: ...
+
+
+class PBag(Generic[T], Sized, Hashable):
+    def __add__(self, other: PBag[T]) -> PBag[T]: ...
+    def __and__(self, other: PBag[T]) -> PBag[T]: ...
+    def __contains__(self, elem: object) -> bool: ...
+    def __hash__(self) -> int: ...
+    def __iter__(self) -> Iterator[T]: ...
+    def __len__(self) -> int: ...
+    def __or__(self, other: PBag[T]) -> PBag[T]: ...
+    def __sub__(self, other: PBag[T]) -> PBag[T]: ...
+    def add(self, elem: T) -> PBag[T]: ...
+    def count(self, elem: T) -> int: ...
+    def remove(self, elem: T) -> PBag[T]: ...
+    def update(self, iterable: Iterable[T]) -> PBag[T]: ...
+
+
+class PDeque(Sequence[T], Hashable):
+    @overload
+    def __getitem__(self, index: int) -> T: ...
+    @overload
+    def __getitem__(self, index: slice) -> PDeque[T]: ...
+    def __hash__(self) -> int: ...
+    def __len__(self) -> int: ...
+    def __lt__(self, other: PDeque[T]) -> bool: ...
+    def append(self, elem: T) -> PDeque[T]: ...
+    def appendleft(self, elem: T) -> PDeque[T]: ...
+    def extend(self, iterable: Iterable[T]) -> PDeque[T]: ...
+    def extendleft(self, iterable: Iterable[T]) -> PDeque[T]: ...
+    @property
+    def left(self) -> T: ...
+    # The real return type is Integral according to what pyrsistent
+    # checks at runtime but mypy doesn't deal in numeric.*:
+    # https://github.com/python/mypy/issues/2636
+    @property
+    def maxlen(self) -> int: ...
+    def pop(self, count: int = 1) -> PDeque[T]: ...
+    def popleft(self, count: int = 1) -> PDeque[T]: ...
+    def remove(self, elem: T) -> PDeque[T]: ...
+    def reverse(self) -> PDeque[T]: ...
+    @property
+    def right(self) -> T: ...
+    def rotate(self, steps: int) -> PDeque[T]: ...
+
+
+class PList(Sequence[T], Hashable):
+    @overload
+    def __getitem__(self, index: int) -> T: ...
+    @overload
+    def __getitem__(self, index: slice) -> PList[T]: ...
+    def __hash__(self) -> int: ...
+    def __len__(self) -> int: ...
+    def __lt__(self, other: PList[T]) -> bool: ...
+    def __gt__(self, other: PList[T]) -> bool: ...
+    def cons(self, elem: T) -> PList[T]: ...
+    @property
+    def first(self) -> T: ...
+    def mcons(self, iterable: Iterable[T]) -> PList[T]: ...
+    def remove(self, elem: T) -> PList[T]: ...
+    @property
+    def rest(self) -> PList[T]: ...
+    def reverse(self) -> PList[T]: ...
+    def split(self, index: int) -> Tuple[PList[T], PList[T]]: ...
+
+T_PClass = TypeVar('T_PClass', bound='PClass')
+
+class PClass(Hashable):
+    def __new__(cls, **kwargs: Any): ...
+    def set(self: T_PClass, *args: Any, **kwargs: Any) -> T_PClass: ...
+    @classmethod
+    def create(
+        cls: Type[T_PClass],
+        kwargs: Any,
+        _factory_fields: Optional[Any] = ...,
+        ignore_extra: bool = ...,
+    ) -> T_PClass: ...
+    def serialize(self, format: Optional[Any] = ...): ...
+    def transform(self, *transformations: Any): ...
+    def __eq__(self, other: object): ...
+    def __ne__(self, other: object): ...
+    def __hash__(self): ...
+    def __reduce__(self): ...
+    def evolver(self) -> PClassEvolver: ...
+    def remove(self: T_PClass, name: Any) -> T_PClass: ...
+
+class PClassEvolver:
+    def __init__(self, original: Any, initial_dict: Any) -> None: ...
+    def __getitem__(self, item: Any): ...
+    def set(self, key: Any, value: Any): ...
+    def __setitem__(self, key: Any, value: Any) -> None: ...
+    def remove(self, item: Any): ...
+    def __delitem__(self, item: Any) -> None: ...
+    def persistent(self) -> PClass: ...
+    def __getattr__(self, item: Any): ...
+
+
+
+class CheckedPMap(PMap[KT, VT]):
+    __key_type__: Type[KT]
+    __value_type__: Type[VT]
+    def __new__(cls, source: Mapping[KT, VT] = ..., size: int = ...) -> CheckedPMap: ...
+    @classmethod
+    def create(cls, source_data: Mapping[KT, VT], _factory_fields: Any = ...) -> CheckedPMap[KT, VT]: ...
+    def serialize(self, format: Optional[Any] = ...) -> Dict[KT, VT]: ...
+
+
+class CheckedPVector(PVector[T]):
+    __type__: Type[T]
+    def __new__(self, initial: Iterable[T] = ...) -> CheckedPVector: ...
+    @classmethod
+    def create(cls, source_data: Iterable[T], _factory_fields: Any = ...) -> CheckedPVector[T]: ...
+    def serialize(self, format: Optional[Any] = ...) -> List[T]: ...
+
+
+class CheckedPSet(PSet[T]):
+    __type__: Type[T]
+    def __new__(cls, initial: Iterable[T] = ...) -> CheckedPSet: ...
+    @classmethod
+    def create(cls, source_data: Iterable[T], _factory_fields: Any = ...) -> CheckedPSet[T]: ...
+    def serialize(self, format: Optional[Any] = ...) -> Set[T]: ...
+
+
+class InvariantException(Exception):
+    invariant_errors: Tuple[Any, ...] = ...  # possibly nested tuple
+    missing_fields: Tuple[str, ...] = ...
+    def __init__(
+        self,
+        error_codes: Any = ...,
+        missing_fields: Any = ...,
+        *args: Any,
+        **kwargs: Any
+    ) -> None: ...
+
+
+class CheckedTypeError(TypeError):
+    source_class: Type[Any]
+    expected_types: Tuple[Any, ...]
+    actual_type: Type[Any]
+    actual_value: Any
+    def __init__(
+        self,
+        source_class: Any,
+        expected_types: Any,
+        actual_type: Any,
+        actual_value: Any,
+        *args: Any,
+        **kwargs: Any
+    ) -> None: ...
+
+
+class CheckedKeyTypeError(CheckedTypeError): ...
+class CheckedValueTypeError(CheckedTypeError): ...
+class CheckedType: ...
+
+
+class PTypeError(TypeError):
+    source_class: Type[Any] = ...
+    field: str = ...
+    expected_types: Tuple[Any, ...] = ...
+    actual_type: Type[Any] = ...
+    def __init__(
+        self,
+        source_class: Any,
+        field: Any,
+        expected_types: Any,
+        actual_type: Any,
+        *args: Any,
+        **kwargs: Any
+    ) -> None: ...
diff --git a/third_party/python/pyrsistent/setup.cfg b/third_party/python/pyrsistent/setup.cfg
new file mode 100644
index 0000000000..e4eba0b6c3
--- /dev/null
+++ b/third_party/python/pyrsistent/setup.cfg
@@ -0,0 +1,7 @@
+[aliases]
+test = pytest
+
+[egg_info]
+tag_build = 
+tag_date = 0
+
diff --git a/third_party/python/pyrsistent/setup.py b/third_party/python/pyrsistent/setup.py
new file mode 100644
index 0000000000..931800ff15
--- /dev/null
+++ b/third_party/python/pyrsistent/setup.py
@@ -0,0 +1,81 @@
+import os
+from setuptools import setup, Extension
+import sys
+import platform
+import warnings
+import codecs
+from distutils.command.build_ext import build_ext
+from distutils.errors import CCompilerError
+from distutils.errors import DistutilsPlatformError, DistutilsExecError
+from _pyrsistent_version import __version__
+
+readme_path = os.path.join(os.path.dirname(__file__), 'README.rst')
+with codecs.open(readme_path, encoding='utf8') as f:
+    readme = f.read()
+
+extensions = []
+if platform.python_implementation() == 'CPython':
+    extensions = [Extension('pvectorc', sources=['pvectorcmodule.c'])]
+
+needs_pytest = {'pytest', 'test', 'ptr'}.intersection(sys.argv)
+pytest_runner = ['pytest-runner'] if needs_pytest else []
+
+
+class custom_build_ext(build_ext):
+    """Allow C extension building to fail."""
+
+    warning_message = """
+********************************************************************************
+WARNING: Could not build the %s.
+         Pyrsistent will still work but performance may be degraded.
+         %s
+********************************************************************************
+"""
+
+    def run(self):
+        try:
+            build_ext.run(self)
+        except Exception:
+            e = sys.exc_info()[1]
+            sys.stderr.write('%s\n' % str(e))
+            sys.stderr.write(self.warning_message % ("extension modules", "There was an issue with your platform configuration - see above."))
+
+    def build_extension(self, ext):
+        name = ext.name
+        try:
+            build_ext.build_extension(self, ext)
+        except Exception:
+            e = sys.exc_info()[1]
+            sys.stderr.write('%s\n' % str(e))
+            sys.stderr.write(self.warning_message % ("%s extension module" % name, "The output above this warning shows how the compilation failed."))
+
+setup(
+    name='pyrsistent',
+    version=__version__,
+    description='Persistent/Functional/Immutable data structures',
+    long_description=readme,
+    author='Tobias Gustafsson',
+    author_email='tobias.l.gustafsson@gmail.com',
+    url='http://github.com/tobgu/pyrsistent/',
+    license='MIT',
+    license_files=['LICENCE.mit'],
+    py_modules=['_pyrsistent_version'],
+    classifiers=[
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: MIT License',
+        'Operating System :: OS Independent',
+        'Programming Language :: Python :: 3.5',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: Implementation :: PyPy',
+    ],
+    test_suite='tests',
+    tests_require=['pytest<5', 'hypothesis<5'],
+    scripts=[],
+    setup_requires=pytest_runner,
+    ext_modules=extensions,
+    cmdclass={'build_ext': custom_build_ext},
+    install_requires=['six'],
+    packages=['pyrsistent'],
+    package_data={'pyrsistent': ['py.typed', '__init__.pyi', 'typing.pyi']},
+)