Cython is a Python-like language that makes it easy to write C-based extensions for Python. This is a Good Thing™, because people who will write good Python wrappers will be fluent in Python, but not necessarily in C. Alternatives like SWIG allow you to specify wrappers in a C-like language, which makes thin wrappers easy, but can lead to a less idomatic wrapper API. I should also point out ctypes, which has the advantage of avoiding compiled wrappers altogether, at the expense of dealing with linking explicitly in the Python code.
The Cython docs are fairly extensive, and I found them to be
sufficient for writing my pycomedi wrapper around the Comedi
library. One annoying thing was that Cython does not support
__all__ (cython-users). I took a stab at fixing this,
but got sidetracked cleaning up the Cython parser (cython-devel,
later in cython-devel). I must have bit off more than I
should have, since I eventually ran out of time to work on merging my
code, and the Cython trunk moved off without me ;).