> Computing intensive, no. Code that is doing a CPU intensive computation but makes no system calls will never release the GIL.

Any code that does not involve Python objects can release the GIL, no matter whether it makes system call or not.

For example, NumPy the most popular scientific computation package in Python, on which many other popular packages like Pandas are based, releases the GIL when doing operation on matrix. This is documented at https://numpy.org/doc/stable/reference/internals.code-explan...:

> If NPY_ALLOW_THREADS is defined during compilation, then as long as no object arrays are involved, the Python Global Interpreter Lock (GIL) is released prior to calling the loops. It is re-acquired if necessary to handle error conditions.

To do so it uses the same macro used by the socket module when doing system calls: https://github.com/numpy/numpy/blob/18a6e3e505ee416ddfc617f3...