A Simple C Extension Module
At least that’s the short story; we need to turn to some code to make this more concrete. C types generally export a C module with a constructor function. Because of that, and because they are simpler, let’s start off by studying the basics of C module coding with a quick example.
As mentioned, when you add new or existing C components to
Python, you need to code an interface (“glue”) logic layer in C that
handles cross-language dispatching and data translation. The C source
file in Example 22-1 shows
how to code one by hand. It implements a simple C extension module
named hello for use in Python
scripts, with a function named message that simply returns its input string
argument with extra text prepended. Python scripts will call this
function as usual, but this one is coded in C, not in Python.
Example 22-1. PP3E\Integrate\Extend\Hello\hello.c
/******************************************************************** * A simple C extension module for Python, called "hello"; compile * this into a ".so" on python path, import and call hello.message; ********************************************************************/ #include <Python.h> #include <string.h> /* module functions */ static PyObject * /* returns object */ message(PyObject *self, PyObject *args) /* self unused in modules */ { /* args from Python call */ char *fromPython, result[64]; if (! PyArg_Parse(args, "(s)", &fromPython)) /* convert Python -> C */ return NULL; /* null=raise exception */ else ...