Overload a member methods for both intance and class in python

Question

I'm working on a python class which has a valid meaning for the index operator ([] or __getitem__() if you would prefer) at both the class and instance level. Specifically indexing strings is valid. As such I would like to implement a dictionary interface for both levels. The __class_getitem__() method solves this problem for the [] operator; However, I will still need other methods such as keys(), __contains__(), __len__() etc to behave differently if you for example call cls.keys() vs cls().keys().

I'm fairly sure this can be done by using some combination of __getattr__() / __getattribute__() overloads and some tricky closure shenanigans. However, I would strongly like avoid doing so if at all reasonible for the following reasons:

• doings so is terribly clunky
• its confusing to non-expert coders
• hard to see and parse to the point of potentially blindsiding expert coders
• Tools like PyCharm's code completion system can't see that kind of stuff.

I suspect that the best answer will probably involve using a metaclass which I'm a bit resigned to but hope there is a clever way to avoid maybe through argument type detection and a decorator or something. (a subclass of classmethod which has a instancemethod attribute which gets called in the case of not isinstance(cls, type) maybe?)

Answer 1

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