:mod:`code` --- Interpreter base classes

========================================

.. module:: code

   :synopsis: Facilities to implement read-eval-print loops.

The ``code`` module provides facilities to implement read-eval-print loops in

Python.  Two classes and convenience functions are included which can be used to

build applications which provide an interactive interpreter prompt.

.. class:: InteractiveInterpreter([locals])

   This class deals with parsing and interpreter state (the user's namespace); it

   does not deal with input buffering or prompting or input file naming (the

   filename is always passed in explicitly). The optional *locals* argument

   specifies the dictionary in which code will be executed; it defaults to a newly

   created dictionary with key ``'__name__'`` set to ``'__console__'`` and key

   ``'__doc__'`` set to ``None``.

.. class:: InteractiveConsole([locals[, filename]])

   Closely emulate the behavior of the interactive Python interpreter. This class

   builds on :class:`InteractiveInterpreter` and adds prompting using the familiar

   ``sys.ps1`` and ``sys.ps2``, and input buffering.

.. function:: interact([banner[, readfunc[, local]]])

   Convenience function to run a read-eval-print loop.  This creates a new instance

   of :class:`InteractiveConsole` and sets *readfunc* to be used as the

   :meth:`raw_input` method, if provided.  If *local* is provided, it is passed to

   the :class:`InteractiveConsole` constructor for use as the default namespace for

   the interpreter loop.  The :meth:`interact` method of the instance is then run

   with *banner* passed as the banner to use, if provided.  The console object is

   discarded after use.

.. function:: compile_command(source[, filename[, symbol]])

   This function is useful for programs that want to emulate Python's interpreter

   main loop (a.k.a. the read-eval-print loop).  The tricky part is to determine

   when the user has entered an incomplete command that can be completed by

   entering more text (as opposed to a complete command or a syntax error).  This

   function *almost* always makes the same decision as the real interpreter main

   loop.

   *source* is the source string; *filename* is the optional filename from which

   source was read, defaulting to ``'<input>'``; and *symbol* is the optional

   grammar start symbol, which should be either ``'single'`` (the default) or

   ``'eval'``.

   Returns a code object (the same as ``compile(source, filename, symbol)``) if the

   command is complete and valid; ``None`` if the command is incomplete; raises

   :exc:`SyntaxError` if the command is complete and contains a syntax error, or

   raises :exc:`OverflowError` or :exc:`ValueError` if the command contains an

   invalid literal.

.. _interpreter-objects:

Interactive Interpreter Objects

-------------------------------

.. method:: InteractiveInterpreter.runsource(source[, filename[, symbol]])

   Compile and run some source in the interpreter. Arguments are the same as for

   :func:`compile_command`; the default for *filename* is ``'<input>'``, and for

   *symbol* is ``'single'``.  One several things can happen:

   * The input is incorrect; :func:`compile_command` raised an exception

     (:exc:`SyntaxError` or :exc:`OverflowError`).  A syntax traceback will be

     printed by calling the :meth:`showsyntaxerror` method.  :meth:`runsource`

     returns ``False``.

   * The input is incomplete, and more input is required; :func:`compile_command`

     returned ``None``. :meth:`runsource` returns ``True``.

   * The input is complete; :func:`compile_command` returned a code object.  The

     code is executed by calling the :meth:`runcode` (which also handles run-time

     exceptions, except for :exc:`SystemExit`). :meth:`runsource` returns ``False``.

   The return value can be used to decide whether to use ``sys.ps1`` or ``sys.ps2``

   to prompt the next line.

.. method:: InteractiveInterpreter.runcode(code)

   Execute a code object. When an exception occurs, :meth:`showtraceback` is called

   to display a traceback.  All exceptions are caught except :exc:`SystemExit`,

   which is allowed to propagate.

   A note about :exc:`KeyboardInterrupt`: this exception may occur elsewhere in

   this code, and may not always be caught.  The caller should be prepared to deal

   with it.

.. method:: InteractiveInterpreter.showsyntaxerror([filename])

   Display the syntax error that just occurred.  This does not display a stack

   trace because there isn't one for syntax errors. If *filename* is given, it is

   stuffed into the exception instead of the default filename provided by Python's

   parser, because it always uses ``'<string>'`` when reading from a string. The

   output is written by the :meth:`write` method.

.. method:: InteractiveInterpreter.showtraceback()

   Display the exception that just occurred.  We remove the first stack item

   because it is within the interpreter object implementation. The output is

   written by the :meth:`write` method.

.. method:: InteractiveInterpreter.write(data)

   Write a string to the standard error stream (``sys.stderr``). Derived classes

   should override this to provide the appropriate output handling as needed.

.. _console-objects:

Interactive Console Objects

---------------------------

The :class:`InteractiveConsole` class is a subclass of

:class:`InteractiveInterpreter`, and so offers all the methods of the

interpreter objects as well as the following additions.

.. method:: InteractiveConsole.interact([banner])

   Closely emulate the interactive Python console. The optional banner argument

   specify the banner to print before the first interaction; by default it prints a

   banner similar to the one printed by the standard Python interpreter, followed

   by the class name of the console object in parentheses (so as not to confuse

   this with the real interpreter -- since it's so close!).

.. method:: InteractiveConsole.push(line)

   Push a line of source text to the interpreter. The line should not have a

   trailing newline; it may have internal newlines.  The line is appended to a

   buffer and the interpreter's :meth:`runsource` method is called with the

   concatenated contents of the buffer as source.  If this indicates that the

   command was executed or invalid, the buffer is reset; otherwise, the command is

   incomplete, and the buffer is left as it was after the line was appended.  The

   return value is ``True`` if more input is required, ``False`` if the line was

   dealt with in some way (this is the same as :meth:`runsource`).

.. method:: InteractiveConsole.resetbuffer()

   Remove any unhandled source text from the input buffer.

.. method:: InteractiveConsole.raw_input([prompt])

   Write a prompt and read a line.  The returned line does not include the trailing

   newline.  When the user enters the EOF key sequence, :exc:`EOFError` is raised.

   The base implementation uses the built-in function :func:`raw_input`; a subclass

   may replace this with a different implementation.