Given that you say "basically glue" why the previous surprise about "basically using C types and GMP" ?
Because it's obviously not the idiomatic way to use Python. No one is going to bother writing a program that way in Python, they'd just write it in C or C++ then link it.
But everyone knows it is significantly faster than Python. Probably at least a few times for pure JS vs. pure Python programs. Not that it matters, Python is basically glue to run mostly C and C++ programs.