Cython is a bit different from CPython / Pythran / Shedskin in that you need to learn the Cython language, which is a Python-ish programming language, but not Python.

Shedskin and Pythran look somewhat similar to me (disclaimer: I've contributed quite a bit to Shedskin but have never used Pythran so far), except in Shedskin you don't even need annotations like with Pythran (the downside being the finer control you have of the native types used is through the transpiler options). Also, Shedskin development is not much active these days — to say the least — and there's zero support for Python 3, while Pythran is under fairly active development has beta support for Python 3.

If you're interested in Python / native implementations, you might be interested by Nuitka as well: http://nuitka.net/