This is Cython and Unifdef wrapper that adds some (very basic) preprocessor support to Cython.

cython_ifdef.py makes it possible to use preprocessor directives right in your .pyx source:

class X:

#ifdef _WIN32
    def windows_only(self):
        return 5
#else
    def unix_only(self):
        return 6
#endif

Running cython_ifdef.py test.pyx will produce a test.c file that includes appropriate #ifdef _WIN32 to produce a class that has windows_only method when _WIN32 is defined and unix_only when it's not.

Here's an example of what cython_ifdef.py can process: gevent/core_.pyx.

Installation

In addition to Cython, you need to have unifdef installed in order to run this script. On Debian/Ubuntu, do apt-get install unifdef.

Download the script from github and put it somewhere on the run path.

How does it work

• It gets lists of all preprocessor symbols used in the source file using unifdef -t -s
• It runs unifdef for all possible configurations on the original source.
• For each generated source, it runs cython and stores the result in memory.
• It then merges all the resulting .c files into one with the appropriate #ifdef in place.

Limitations

• It only supports symbols that are either defined or undefined. Processing expressions such as #if SYMBOL == 5 is not implemented.
• It does not look into included .pxi.
• The amount of time it takes is exponential: 2^(Number of symbols), so it does not support arbitrary amount of preprocessor symbols.

It was written to support gevent's use case rather than a generic tool, so be warned.

Author

cython_ifdef.py is written by Denis Bilenko for gevent project and is licensed under MIT license.