Does running separate python processes avoid the GIL?

Question

I'm curious in how the Global Interpreter Lock in python actually works. If I have a c++ application launch four separate instances of a python script will they run in parallel on separate cores, or does the GIL go even deeper then just the single process that was launched and control all python process's regardless of the process that spawned it?

Answer 1

The GIL only affects threads within a single process. The multiprocessing module is in fact an alternative to threading that lets Python programs use multiple cores &c. Your scenario will easily allow use of multiple cores, too.

Answer 2

As Alex Martelli points out you can indeed avoid the GIL by running multiple processes, I just want to add and point out that the GIL is a limitation of the implementation (CPython) and not of Python in general, it's possible to implement Python without this limitation. Stackless Python comes to mind.