How to find type parameter with respect to a specific base?

[wouterdb]

Problem

I have a generic type that wants to know its own generic parameter at runtime.
I can only get this to work in simple cases.

I also tried to capture it by overriding __class_get_item__ but that didn't work.

I there any way to capture the type parameter?

Example

class Reference[T]:

    @classmethod
    def get_reference_type(cls) -> type[T] | None:
        # this will work only when directly extending Reference[T]
        for g in cls.__orig_bases__:  # type: ignore
            if typing_inspect.is_generic_type(g) and typing.get_origin(g) == Reference:
               return typing.get_args(g)[0]


class Test(Reference[str]):
    pass

print(Test.get_reference_type()) # <class 'str'>

class Test2[T](Reference[T]):
    pass

class Tx(Test2[str]):
    pass

print(Tx.get_reference_type()) # None

Ideal solution

print(typing_inspect.parameter_in_base(Test, Reference))  # <class 'str'>
print(typing_inspect.parameter_in_base(Test2[str], Reference))  # <class 'str'>
print(typing_inspect.parameter_in_base(Tx, Reference))  # <class 'str'>

I don't know if this is even possible.

[wouterdb]

I found this issues, python/typing#629

Can I conclude from that that this is currently not possible?