Python Callables is what I want to pass around to C extension. [Stack Overflow question](https://stackoverflow.com/questions/53215786/when-writing-a-python-extension-in-c-how-does-one-pass-a-python-function-in-to#:~:text=The%20Python%20callable%20passed%20in%20will%20be%20a,signature%20of%20your%20function%20pointer.%20As%20an%20example%3A) Section 1.6 of [Python Docs](https://docs.python.org/3/extending/extending.html)
