Is type variable supported for the dispatch?

[snwnde]

Consider the defined type variables,

K = TypeVar('K')
V = TypeVar('V')

and a custom generic dictionary,

class MyGenericDict(collections.UserDict[K, V]):
    ...

I am trying to define,

class MyGenericDict(collections.UserDict[K, V]):
    
    @multimethod.multimethod
    def __mul__(self, other: MyGenericDict[K, Any]):
        return self.__class__({key: value * other[key] for key, value in self.items()})

    @multimethod.multimethod
    def __mul__(self, other: V):
        return self.__class__({key: value * other for key, value in self.items()})

It seems that as long as other is not an instance of MyGenericDict, the call is dispatched to the second definition, no matter if it is an instance of the actual concrete V.

Is this a limitation of the typing system in python, or that of the multimethod package? Or have I done something wrong?

[coady]

There are no constraints on TypeVar('V'), so it matches anything.

[snwnde]

Thanks. Is there way to match int for MyGenericDict[str, int], float for MyGenericDict[str, float] and any type V for MyGenericDict[str, V] or not? From what I understood it seems impossible since V cannot be bound.

[coady]

V can be bound: TypeVar('V', int, float).

Or MyGenericDict[str, int] and MyGenericDict[str, float] can be used.

[snwnde]

Well, this would not work for generally unbound V, which could be int, float, another parameterisation of MyGenericDict or anything else. That said, this design might just be bad and I feel this should not be the way to go. I need to think more. Thank you for your answers!