:mod:`codeop` --- Compile Python code

.. module:: codeop
   :synopsis: Compile (possibly incomplete) Python code.

.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>

.. sectionauthor:: Michael Hudson <mwh@python.net>

The :mod:`codeop` module provides utilities upon which the Python read-eval-print loop can be emulated, as is done in the :mod:`code` module. As a result, you probably don't want to use the module directly; if you want to include such a loop in your program you probably want to use the :mod:`code` module instead.

There are two parts to this job:

1. Being able to tell if a line of input completes a Python statement: in short, telling whether to print '>>>' or '...' next.
2. Remembering which future statements the user has entered, so subsequent input can be compiled with these in effect.

The :mod:`codeop` module provides a way of doing each of these things, and a way of doing them both.

To do just the former:

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

   Tries to compile *source*, which should be a string of Python code and return a
   code object if *source* is valid Python code. In that case, the filename
   attribute of the code object will be *filename*, which defaults to
   ``'<input>'``. Returns ``None`` if *source* is *not* valid Python code, but is a
   prefix of valid Python code.

   If there is a problem with *source*, an exception will be raised.
   :exc:`SyntaxError` is raised if there is invalid Python syntax, and
   :exc:`OverflowError` or :exc:`ValueError` if there is an invalid literal.

   The *symbol* argument determines whether *source* is compiled as a statement
   (``'single'``, the default) or as an :term:`expression` (``'eval'``).  Any
   other value will cause :exc:`ValueError` to  be raised.

   .. note::

      It is possible (but not likely) that the parser stops parsing with a
      successful outcome before reaching the end of the source; in this case,
      trailing symbols may be ignored instead of causing an error.  For example,
      a backslash followed by two newlines may be followed by arbitrary garbage.
      This will be fixed once the API for the parser is better.

Instances of this class have :meth:`__call__` methods identical in signature to the built-in function :func:`compile`, but with the difference that if the instance compiles program text containing a :mod:`__future__` statement, the instance 'remembers' and compiles all subsequent program texts with the statement in force.

Instances of this class have :meth:`__call__` methods identical in signature to :func:`compile_command`; the difference is that if the instance compiles program text containing a __future__ statement, the instance 'remembers' and compiles all subsequent program texts with the statement in force.

A note on version compatibility: the :class:`Compile` and :class:`CommandCompiler` are new in Python 2.2. If you want to enable the future-tracking features of 2.2 but also retain compatibility with 2.1 and earlier versions of Python you can either write

try:
    from codeop import CommandCompiler
    compile_command = CommandCompiler()
    del CommandCompiler
except ImportError:
    from codeop import compile_command

which is a low-impact change, but introduces possibly unwanted global state into your program, or you can write:

try:
    from codeop import CommandCompiler
except ImportError:
    def CommandCompiler():
        from codeop import compile_command
        return compile_command

and then call CommandCompiler every time you need a fresh compiler object.