There are many ways to exploit multi-cores, multi-threading is just one of them. Many other techniques exist. Also, one thing to realize is that if speed really

There are many ways to exploit multi-cores, multi-threading is just one of them. Many other techniques exist. Also, one thing to realize is that if speed really matters (like in scientific apps), you will get much higher speed increase by rewriting some parts in C than by allowing using all the cores from python (at least with only a couple of cores). Finally, a point which is not often brought but is crucial in my opinion is about C extension: the GIL makes C extensions much easier to write. That's one big reason for python success in the first place.