Programming Python, Second Edition

The SWIG Integration Code Generator

But don’t do that. I’m introducing C extension basics so you understand the underlying structure, but today, C extensions are usually better and more easily implemented with the SWIG integration code generator.

SWIG -- the Simplified Wrapper and Interface Generator -- is an open source system created by Dave Beazley. It uses C and C++ type declarations to generate complete C extension modules that integrate existing libraries for use in Python scripts. The generated C extension modules are complete: they automatically handle data conversion, error protocols, reference-count management, and more.

That is, SWIG automatically generates all the “glue” code needed to plug C and C++ components into Python programs; simply compile its output and your extension work is done. You still have to manage compilation and linking details, but the rest of the C extension task is done by SWIG.

A Simple SWIG Example

For instance, instead of writing all that C code in the prior section, write the C function you want to use from Python without any Python integration logic at all, as though it is to be used from C alone. This is illustrated in Example 19-4.

Example 19-4. PP2E\Integrate\Extend\HelloLib\hellolib.c

/********************************************************************* * A simple C library file, with a single function, "message", * which is to be made available for use in Python programs. * There is nothing about Python here--this C function can be ...