Stackless Python is an enhanced version of the Python programming language. It allows programmers to reap the benefits of thread-based programming without the performance and complexity problems associated with conventional threads. The microthreads that Stackless adds to Python are a cheap and lightweight convenience which can if used properly, give the following benefits:

* Improved program structure.
* More readable code.
* Increased programmer productivity.

http://code.google.com/p/pspstacklesspython/