Simple Python Example

$Header: /cvs/projects/SWIG/Examples/python/simple/index.html,v 1.1 2000/06/17 21:40:59 beazley Exp $

This example illustrates how you can hook Python to a very simple C program containing a function and a global variable.

The C Code

Suppose you have the following C code:
/* File : example.c */

/* A global variable */
double Foo = 3.0;

/* Compute the greatest common divisor of positive integers */
int gcd(int x, int y) {
  int g;
  g = y;
  while (x > 0) {
    g = x;
    x = y % x;
    y = g;
  return g;

The SWIG interface

Here is a simple SWIG interface file:
/* File: example.i */
%module example

extern int gcd(int x, int y);
extern double Foo;


  1. swig -python example.i

  2. Compile example_wrap.c and example.c to create the extension

Using the extension

Click here to see a script that calls our C functions from Python.

Key points

  • Use the import statement to load your extension module from Python. For example:
    import example
  • C functions work just like Python functions. For example:
    g = example.gcd(42,105)
  • C global variables are accessed through a special variable called 'cvar'. For example:
    a = example.cvar.Foo