Popular third party extension modules

To test C API changes in Python, it's useful to test a bunch of popular extension modules to check if they still build.

Cython

The first important candidate is Cython, many projects use it:

Cython
lxml
numpy (Cython + C API)
pandas
pyzmq (for Jupyter)
scipy

Python C API

Use directly the C API:

Mercurial
Pillow
cffi
psycopg2