I'm convinced that this is a hard task, hard enough that probably no one will do it properly. But for emulating Python class semantics, is there any reason why we can't:

1. Come up with an inefficient but exact modelling of the semantics in pure Lua using tables and metamethods. I think I can write metamethods showing exactly the behaviour you describe.

2.Come up with an efficient implementation of python_class userdata?

The problem you describe is the problem of really understanding what's going on, not a deficit in Lua's ability to model it.