Extending Python
It turns out that writing C modules for Python is really trivial. I spent quite a while the other day trying to figure out how to compile and link everything, but it turns out that the distutils module will take care of all this for you.
The trick is to make a setup.py file that looks like this:
from distutils.core import setup, Extension
setup(name="foo", version="1.0",
ext_modules=[Extension("foo", ["foo.c"])])
(That example comes from the Python manual).
Now, when you run python setup.py build, it will invoke GCC or MSVC (your platform's default C compiler) and build you a .so or a .dll out of foo.c
Here's an example of the sort of C code you have to write to be callable from Python. You also need to register your module with the Python interpreter - more on that later.