Building an extension module with SWIG

[garyr]

I'm trying to create an extension module using SWIG. I've
succeeded in generating a pyd file but when I import the module I get the
error message: "SystemError: dynamic module not initialized properly." I
added an initfoo() function but that didn't solve the problem. Below are the
various files, a slightly modified version of a SWIG exmaple.
I'm using Python 2.7

What am I missing?

//foo.c:
#include "foo.h"
double Foo;
void initfoo()
{
    Foo = 3.0;
}
int gcd(int x, int y) {
  int g;
  g = y;
  while (x > 0) {
    g = x;
    x = y % x;
    y = g;
  }
  return g;
}

#foo.h:
extern void initfoo();
extern double Foo;
extern int gcd(int x, int y);

#foo.i:
%module example
%inline %{
extern int    gcd(int x, int y);
extern double Foo;
%}

#setup.py
from setuptools import setup, Extension
setup(name='foo',
    version='0.1',
    ext_modules=[Extension('foo', ['foo.c', 'foo.i'],
                    include_dirs=['.'],
                    depends=['foo.h', 'foo.i'],
                    swig_opts=['-modern', '-I../include'],
                    )],
    )