As in my sibling comment, pypy has already done all this work.

CPython's struct module is just a shim importing the C implementations: https://github.com/python/cpython/blob/main/Lib/struct.py

Pypy's is a Python(-ish) implementation, leveraging primitives from its own rlib and pypy.interpreter spaces: https://github.com/pypy/pypy/blob/main/pypy/module/struct/in...

The Python stdlib has enormous surface area, and of course it's also a moving target.

Aah, neat! Yeah, piggy-backing off pypy's work here would probably make the most sense.

It'll also be interesting to see how OP deals with things like dictionaries and lists.