Not surprising - many Python built-ins are implemented in C. And for any numerical or computational libraries, doing it in C is all but essential.
Tangential, but this is why NumPy totally changed my workflow. I can use all of the benefits of Python, including its libraries and syntax, and still have a program that executes at the speed of C, rather than Python[1].
[1] Not literally the speed of C, but you get the idea.
