[WIP, DO NOT MERGE] bpo-41188: Prepare CPython for opague PyObject structure. by WildCard65 · Pull Request #21262 · python/cpython

As it stands, functions like _Py_TYPE, _Py_SIZE, _Py_INCREF, _Py_DECREF rely on "PyObject" being a complete type. Opaque objects on the other hand are classified as incomplete types.

Incomplete types can't be used for anything but pointers (*) and references (&), these functions will fail when PyObject goes opaque in the limited API, infact, sizeof() also fails on incomplete types.

The purpose of the static library is not to be a different flavour of Python, but to act as a bridge into Python's internals while respecting the limitations of incomplete types, while also eliminating function call overhead.

As an added bonus, this static library can be "reskinned" for runtimes that take a different approach to PyObject (if any) and descendant built-in types while end users don't have to worry about what the runtime's schematic is.