"Python-stackless avoids this problem" Not really. Stackless Python still has a GIL, and if you want to make use of multiple threads, the GIL will still bite

"Python-stackless avoids this problem" Not really. Stackless Python still has a GIL, and if you want to make use of multiple threads, the GIL will still bite you. Stackless allows you to write coroutines and has lots of cool abilities, but avoiding the GIL is simply not one of them as far as making use of multiple cores.