29.2. "codeop" — Compile Python code
************************************

The "codeop" module provides utilities upon which the Python read-
eval-print loop can be emulated, as is done in the "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 "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 "codeop" module provides a way of doing each of these things, and
a way of doing them both.

To do just the former:

codeop.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.
   "SyntaxError" is raised if there is invalid Python syntax, and
   "OverflowError" or "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 "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.

class codeop.Compile

   Instances of this class have "__call__()" methods identical in
   signature to the built-in function "compile()", but with the
   difference 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.

class codeop.CommandCompiler

   Instances of this class have "__call__()" methods identical in
   signature to "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 "Compile" and "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.
