C Module - traditional way. Write your functions in C (usually just wrapper code).
CTypes - newer way since 2006. Integration a bit more difficult. Great to use if don’t need Python types, exceptions, & objects back.
CDLL: reference to DLL
Init module that sets up the module.
Pypy: libraries written in C may not work. No need to change Python code.
Pure C: 11.2x faster, Pypy: 5.7x faster.