Adding upstream version 3.0.36.upstream/3.0.36upstream

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

1 files changed, 341 insertions, 0 deletions

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+.. _tutorial_repl:
+
+Tutorial: Build an SQLite REPL
+==============================
+
+The aim of this tutorial is to build an interactive command line interface for
+an SQLite database using prompt_toolkit_.
+
+First, install the library using pip, if you haven't done this already.
+
+.. code::
+
+    pip install prompt_toolkit
+
+
+Read User Input
+---------------
+
+Let's start accepting input using the
+:func:`~prompt_toolkit.shortcuts.prompt()` function. This will ask the user for
+input, and echo back whatever the user typed. We wrap it in a ``main()``
+function as a good practice.
+
+.. code:: python
+
+    from prompt_toolkit import prompt
+
+    def main():
+        text = prompt('> ')
+        print('You entered:', text)
+
+    if __name__ == '__main__':
+        main()
+
+.. image:: ../../images/repl/sqlite-1.png
+
+
+Loop The REPL
+-------------
+
+Now we want to call the :meth:`~prompt_toolkit.shortcuts.PromptSession.prompt`
+method in a loop. In order to keep the history, the easiest way to do it is to
+use a :class:`~prompt_toolkit.shortcuts.PromptSession`. This uses an
+:class:`~prompt_toolkit.history.InMemoryHistory` underneath that keeps track of
+the history, so that if the user presses the up-arrow, they'll see the previous
+entries.
+
+The :meth:`~prompt_toolkit.shortcuts.PromptSession.prompt` method raises
+``KeyboardInterrupt`` when ControlC has been pressed and ``EOFError`` when
+ControlD has been pressed. This is what people use for cancelling commands and
+exiting in a REPL. The try/except below handles these error conditions and make
+sure that we go to the next iteration of the loop or quit the loop
+respectively.
+
+.. code:: python
+
+    from prompt_toolkit import PromptSession
+
+    def main():
+        session = PromptSession()
+
+        while True:
+            try:
+                text = session.prompt('> ')
+            except KeyboardInterrupt:
+                continue
+            except EOFError:
+                break
+            else:
+                print('You entered:', text)
+        print('GoodBye!')
+
+    if __name__ == '__main__':
+        main()
+
+.. image:: ../../images/repl/sqlite-2.png
+
+
+Syntax Highlighting
+-------------------
+
+This is where things get really interesting. Let's step it up a notch by adding
+syntax highlighting to the user input. We know that users will be entering SQL
+statements, so we can leverage the Pygments_ library for coloring the input.
+The ``lexer`` parameter allows us to set the syntax lexer. We're going to use
+the ``SqlLexer`` from the Pygments_ library for highlighting.
+
+Notice that in order to pass a Pygments lexer to prompt_toolkit, it needs to be
+wrapped into a :class:`~prompt_toolkit.lexers.PygmentsLexer`.
+
+.. code:: python
+
+    from prompt_toolkit import PromptSession
+    from prompt_toolkit.lexers import PygmentsLexer
+    from pygments.lexers.sql import SqlLexer
+
+    def main():
+        session = PromptSession(lexer=PygmentsLexer(SqlLexer))
+
+        while True:
+            try:
+                text = session.prompt('> ')
+            except KeyboardInterrupt:
+                continue
+            except EOFError:
+                break
+            else:
+                print('You entered:', text)
+        print('GoodBye!')
+
+    if __name__ == '__main__':
+        main()
+
+.. image:: ../../images/repl/sqlite-3.png
+
+
+Auto-completion
+---------------
+
+Now we are going to add auto completion. We'd like to display a drop down menu
+of `possible keywords <https://www.sqlite.org/lang_keywords.html>`_ when the
+user starts typing.
+
+We can do this by creating an `sql_completer` object from the
+:class:`~prompt_toolkit.completion.WordCompleter` class, defining a set of
+`keywords` for the auto-completion.
+
+Like the lexer, this ``sql_completer`` instance can be passed to either the
+:class:`~prompt_toolkit.shortcuts.PromptSession` class or the
+:meth:`~prompt_toolkit.shortcuts.PromptSession.prompt` method.
+
+.. code:: python
+
+    from prompt_toolkit import PromptSession
+    from prompt_toolkit.completion import WordCompleter
+    from prompt_toolkit.lexers import PygmentsLexer
+    from pygments.lexers.sql import SqlLexer
+
+    sql_completer = WordCompleter([
+        'abort', 'action', 'add', 'after', 'all', 'alter', 'analyze', 'and',
+        'as', 'asc', 'attach', 'autoincrement', 'before', 'begin', 'between',
+        'by', 'cascade', 'case', 'cast', 'check', 'collate', 'column',
+        'commit', 'conflict', 'constraint', 'create', 'cross', 'current_date',
+        'current_time', 'current_timestamp', 'database', 'default',
+        'deferrable', 'deferred', 'delete', 'desc', 'detach', 'distinct',
+        'drop', 'each', 'else', 'end', 'escape', 'except', 'exclusive',
+        'exists', 'explain', 'fail', 'for', 'foreign', 'from', 'full', 'glob',
+        'group', 'having', 'if', 'ignore', 'immediate', 'in', 'index',
+        'indexed', 'initially', 'inner', 'insert', 'instead', 'intersect',
+        'into', 'is', 'isnull', 'join', 'key', 'left', 'like', 'limit',
+        'match', 'natural', 'no', 'not', 'notnull', 'null', 'of', 'offset',
+        'on', 'or', 'order', 'outer', 'plan', 'pragma', 'primary', 'query',
+        'raise', 'recursive', 'references', 'regexp', 'reindex', 'release',
+        'rename', 'replace', 'restrict', 'right', 'rollback', 'row',
+        'savepoint', 'select', 'set', 'table', 'temp', 'temporary', 'then',
+        'to', 'transaction', 'trigger', 'union', 'unique', 'update', 'using',
+        'vacuum', 'values', 'view', 'virtual', 'when', 'where', 'with',
+        'without'], ignore_case=True)
+
+    def main():
+        session = PromptSession(
+            lexer=PygmentsLexer(SqlLexer), completer=sql_completer)
+
+        while True:
+            try:
+                text = session.prompt('> ')
+            except KeyboardInterrupt:
+                continue
+            except EOFError:
+                break
+            else:
+                print('You entered:', text)
+        print('GoodBye!')
+
+    if __name__ == '__main__':
+        main()
+
+.. image:: ../../images/repl/sqlite-4.png
+
+In about 30 lines of code we got ourselves an auto completing, syntax
+highlighting REPL. Let's make it even better.
+
+
+Styling the menus
+-----------------
+
+If we want, we can now change the colors of the completion menu. This is
+possible by creating a :class:`~prompt_toolkit.styles.Style` instance and
+passing it to the :meth:`~prompt_toolkit.shortcuts.PromptSession.prompt`
+function.
+
+.. code:: python
+
+    from prompt_toolkit import PromptSession
+    from prompt_toolkit.completion import WordCompleter
+    from prompt_toolkit.lexers import PygmentsLexer
+    from prompt_toolkit.styles import Style
+    from pygments.lexers.sql import SqlLexer
+
+    sql_completer = WordCompleter([
+        'abort', 'action', 'add', 'after', 'all', 'alter', 'analyze', 'and',
+        'as', 'asc', 'attach', 'autoincrement', 'before', 'begin', 'between',
+        'by', 'cascade', 'case', 'cast', 'check', 'collate', 'column',
+        'commit', 'conflict', 'constraint', 'create', 'cross', 'current_date',
+        'current_time', 'current_timestamp', 'database', 'default',
+        'deferrable', 'deferred', 'delete', 'desc', 'detach', 'distinct',
+        'drop', 'each', 'else', 'end', 'escape', 'except', 'exclusive',
+        'exists', 'explain', 'fail', 'for', 'foreign', 'from', 'full', 'glob',
+        'group', 'having', 'if', 'ignore', 'immediate', 'in', 'index',
+        'indexed', 'initially', 'inner', 'insert', 'instead', 'intersect',
+        'into', 'is', 'isnull', 'join', 'key', 'left', 'like', 'limit',
+        'match', 'natural', 'no', 'not', 'notnull', 'null', 'of', 'offset',
+        'on', 'or', 'order', 'outer', 'plan', 'pragma', 'primary', 'query',
+        'raise', 'recursive', 'references', 'regexp', 'reindex', 'release',
+        'rename', 'replace', 'restrict', 'right', 'rollback', 'row',
+        'savepoint', 'select', 'set', 'table', 'temp', 'temporary', 'then',
+        'to', 'transaction', 'trigger', 'union', 'unique', 'update', 'using',
+        'vacuum', 'values', 'view', 'virtual', 'when', 'where', 'with',
+        'without'], ignore_case=True)
+
+    style = Style.from_dict({
+        'completion-menu.completion': 'bg:#008888 #ffffff',
+        'completion-menu.completion.current': 'bg:#00aaaa #000000',
+        'scrollbar.background': 'bg:#88aaaa',
+        'scrollbar.button': 'bg:#222222',
+    })
+
+    def main():
+       session = PromptSession(
+           lexer=PygmentsLexer(SqlLexer), completer=sql_completer, style=style)
+
+       while True:
+           try:
+               text = session.prompt('> ')
+           except KeyboardInterrupt:
+               continue
+           except EOFError:
+               break
+           else:
+               print('You entered:', text)
+       print('GoodBye!')
+
+    if __name__ == '__main__':
+        main()
+
+.. image:: ../../images/repl/sqlite-5.png
+
+All that's left is hooking up the sqlite backend, which is left as an exercise
+for the reader. Just kidding... Keep reading.
+
+
+Hook up Sqlite
+--------------
+
+This step is the final step to make the SQLite REPL actually work. It's time
+to relay the input to SQLite.
+
+Obviously I haven't done the due diligence to deal with the errors. But it
+gives a good idea of how to get started.
+
+.. code:: python
+
+    #!/usr/bin/env python
+    import sys
+    import sqlite3
+
+    from prompt_toolkit import PromptSession
+    from prompt_toolkit.completion import WordCompleter
+    from prompt_toolkit.lexers import PygmentsLexer
+    from prompt_toolkit.styles import Style
+    from pygments.lexers.sql import SqlLexer
+
+    sql_completer = WordCompleter([
+        'abort', 'action', 'add', 'after', 'all', 'alter', 'analyze', 'and',
+        'as', 'asc', 'attach', 'autoincrement', 'before', 'begin', 'between',
+        'by', 'cascade', 'case', 'cast', 'check', 'collate', 'column',
+        'commit', 'conflict', 'constraint', 'create', 'cross', 'current_date',
+        'current_time', 'current_timestamp', 'database', 'default',
+        'deferrable', 'deferred', 'delete', 'desc', 'detach', 'distinct',
+        'drop', 'each', 'else', 'end', 'escape', 'except', 'exclusive',
+        'exists', 'explain', 'fail', 'for', 'foreign', 'from', 'full', 'glob',
+        'group', 'having', 'if', 'ignore', 'immediate', 'in', 'index',
+        'indexed', 'initially', 'inner', 'insert', 'instead', 'intersect',
+        'into', 'is', 'isnull', 'join', 'key', 'left', 'like', 'limit',
+        'match', 'natural', 'no', 'not', 'notnull', 'null', 'of', 'offset',
+        'on', 'or', 'order', 'outer', 'plan', 'pragma', 'primary', 'query',
+        'raise', 'recursive', 'references', 'regexp', 'reindex', 'release',
+        'rename', 'replace', 'restrict', 'right', 'rollback', 'row',
+        'savepoint', 'select', 'set', 'table', 'temp', 'temporary', 'then',
+        'to', 'transaction', 'trigger', 'union', 'unique', 'update', 'using',
+        'vacuum', 'values', 'view', 'virtual', 'when', 'where', 'with',
+        'without'], ignore_case=True)
+
+    style = Style.from_dict({
+        'completion-menu.completion': 'bg:#008888 #ffffff',
+        'completion-menu.completion.current': 'bg:#00aaaa #000000',
+        'scrollbar.background': 'bg:#88aaaa',
+        'scrollbar.button': 'bg:#222222',
+    })
+
+    def main(database):
+        connection = sqlite3.connect(database)
+        session = PromptSession(
+            lexer=PygmentsLexer(SqlLexer), completer=sql_completer, style=style)
+
+        while True:
+            try:
+                text = session.prompt('> ')
+            except KeyboardInterrupt:
+                continue  # Control-C pressed. Try again.
+            except EOFError:
+                break  # Control-D pressed.
+
+            with connection:
+                try:
+                    messages = connection.execute(text)
+                except Exception as e:
+                    print(repr(e))
+                else:
+                    for message in messages:
+                        print(message)
+
+        print('GoodBye!')
+
+    if __name__ == '__main__':
+        if len(sys.argv) < 2:
+            db = ':memory:'
+        else:
+            db = sys.argv[1]
+
+        main(db)
+
+.. image:: ../../images/repl/sqlite-6.png
+
+I hope that gives an idea of how to get started on building command line
+interfaces.
+
+The End.
+
+.. _prompt_toolkit: https://github.com/prompt-toolkit/python-prompt-toolkit
+.. _Pygments: http://pygments.org/