The second argument to the Extension constructor is a list of source files. Since the Distutils currently only support C/C++ extensions, these are normally C/C++ source files. (Be sure to use appropriate extensions to distinguish C++ source files: .cc and .cpp seem to be recognized by both Unix and Windows compilers.)
However, you can also include SWIG interface (.i) files in the
build_ext command knows how to deal with SWIG
extensions: it will run SWIG on the interface file and compile the
resulting C/C++ file into your extension.
** SWIG support is rough around the edges and largely untested; especially SWIG support of C++ extensions! Explain in more detail here when the interface firms up. **
On some platforms, you can include non-source files that are processed by the compiler and included in your extension. Currently, this just means Windows resource files for Visual C++. ** get more detail on this feature from Thomas Heller! **