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future-import-boilerplate
=========================
Most Python files should include the following boilerplate at the top of the file, right after the
comment header:
.. code-block:: python
from __future__ import (absolute_import, division, print_function)
This uses Python 3 semantics for absolute versus relative imports, division, and print. By doing this,
we can write code which is portable between Python 2 and Python 3 by following the Python 3 semantics.
absolute_import
---------------
When Python 2 encounters an import of a name in a file like ``import copy`` it attempts to load
``copy.py`` from the same directory as the file is in. This can cause problems if there is a python
file of that name in the directory and also a python module in ``sys.path`` with that same name. In
that case, Python 2 would load the one in the same directory and there would be no way to load the
one on ``sys.path``. Python 3 fixes this by making imports absolute by default. ``import copy``
will find ``copy.py`` from ``sys.path``. If you want to import ``copy.py`` from the same directory,
the code needs to be changed to perform a relative import: ``from . import copy``.
.. seealso::
* `Absolute and relative imports <https://www.python.org/dev/peps/pep-0328>`_
division
--------
In Python 2, the division operator (``/``) returns integer values when used with integers. If there
was a remainder, this part would be left off (aka, `floor division`). In Python 3, the division
operator (``/``) always returns a floating point number. Code that needs to calculate the integer
portion of the quotient needs to switch to using the floor division operator (`//`) instead.
.. seealso::
* `Changing the division operator <https://www.python.org/dev/peps/pep-0238>`_
print_function
--------------
In Python 2, :func:`python:print` is a keyword. In Python 3, :func:`python3:print` is a function with different
parameters. Using this ``__future__`` allows using the Python 3 print semantics everywhere.
.. seealso::
* `Make print a function <https://www.python.org/dev/peps/pep-3105>`_
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