cpyext is the implementation of the C API in PyPy.

See Ronan Lamy's talk Adventures in compatibility emulating CPython's C API in PyPy (YouTube video) at EuroPython 2018.

See pypy/module/cpyext/ and cpyext/stubs.py.

cpyext has unit tests written in Python.

PyPy with cpyext remains slower than CPython.

XXX how much?

See :ref:`Borrowed references <borrowed-ref>`.

Already done in cpyext.