This seems to still miss the critical mechanism that metaclasses provide to the language. There are many ways to enforce a constraint from dervied classes to b

This seems to still miss the critical mechanism that metaclasses provide to the language. There are many ways to enforce a constraint from dervied classes to base classes. Metaclasses are the only* way to enforce a constraint from a base class to a derived class. (* there's actually another way, but don't do it.)