You get a 4x speedup with multicore, and get a 100x slowdown for using Python. Furthermore, Python supports multiple cores perfectly well as long as you use multiple processes. Python threads also work fine for I/O. The only thing it doesn't do is shared memory parallelism. Maybe staying within one process gives you an x% speedup compared to the overhead of sending data between processes, but it simply does not make much sense compared to the 100x. If you need that kind of performance you would not use Python.