Clean and efficient concurrency primitives? I think not? I would be very interested if that is indeed the case.

PyPy supports greenlets and a Stackless Python-style CSP with tasklets and channels. See http://doc.pypy.org/en/latest/stackless.html . And it has for years. The original Stackless author is also one of the PyPy developers.

Or do you mean some other style of concurrency primitives?

Stackless Python has very clean and efficient concurency primitives, something lot of people dont seem to know..

> Stackless Python has very clean and efficient concurency primitives, ....

Sounds like a good topic for a post (or at least a link - hint, hint).

There are plenty of examples on http://www.stackless.com/ :)

I like Cython, but how do you do CSP (Communicating Sequential Processes) with it?

With PyCSP, as one possible example

https://code.google.com/p/pycsp/