[ameliaquining]

Python functions implemented in C can release the GIL when they're doing something that doesn't directly involve manipulating Python objects, and then re-acquire it when they're done: https://docs.python.org/3/c-api/init.html#thread-state-and-t...

All I/O functions in the standard library do this when blocked.

[hot_gril]

This is a far better explanation than the usual opaque "it's concurrent but not parallel" that I'd argue isn't even correct (cause two C calls on separate threads are running in parallel if they don't hold the GIL). Or "it's multithreading but not multiprocessing" which misses the point.