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Doc/library/codeop.rst

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+
+: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>
+
+
+.. % LaTeXed from excellent doc-string.
+
+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:
+
+#. Being able to tell if a line of input completes a Python  statement: in
+   short, telling whether to print '``>>>``' or '``...``' next.
+
+#. 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 expression (``'eval'``).  Any other value
+   will cause :exc:`ValueError` to  be raised.
+
+   **Caveat:** 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.
+
+
+.. class:: Compile()
+
+   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.
+
+
+.. class:: CommandCompiler()
+
+   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.
+