[issue38978] Implement __class_getitem__ for Future, Task, Queue

[Andrew Svetlov]

Andrew Svetlov <andrew.svetlov at gmail.com> added the comment:

I thought __class_getitem__ was invented exactly to simplify generic types support.

The only thing that confuses me an example from PEP 560:

class MyList:
    def __getitem__(self, index):
        return index + 1
    def __class_getitem__(cls, item):
        return f"{cls.__name__}[{item.__name__}]"

It prevents from instantiating a generic on inheritance, e.g. the following code raises TypeError:

class MyOtherList(MyList[int]):
    pass

It would be nice if Ivan clarifies what is the best practice in this case.
I think the method should return unmodified class, not a string.

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<https://bugs.python.org/issue38978>
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