Comment by onesphere

As a compiler, python is an optimized (C/kernel) implementation of parse generation. JIT (PyPy) is a method that parses a 'trace' variation of grammar instead of syntax, where the optimizer compiles source objects that are not limited to python code.

It's goal is to create as many 'return' instructions as it can decide to.

GIL is merely a CPython problem but synchronization can also be a compilation problem.