27.2 codeop -- Compile Python code

27.2 `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:

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 codeop module provides a way of doing each of these things, and a way of doing them both.

To do just the former:

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.

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 __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 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.

See About this document... for information on suggesting changes.