A 100M LLM is already in the same order of magnitude of Landauer's estimate for the functionnal memory capacity (10^9). But anyway I suppose the question is not about memorizing all the information within your code but just to gain some understanding of the moving parts. If that's so a very small toy model would be enough.

Moreover if we see your python code as an unvompressed version of the LLMs, provided the compression ratio is high in a modern LLM, you have to start with a tiny LLM to finish with a python code of reasonable size.

A preliminary question would be : what is the maximum size of clear python code understable for a competent developer.