Inner/Nested Class Within Function Return Type Not Defined

[jodhus]

Apologies for the title word salad.

I have a static class factory function that I defined as returning the inner class; however, I'm getting mixed results with type checking:

def class_factory() -> "InnerClass":
    class InnerClass:
        pass
    return InnerClass

Pylint seems to have no problem, but Mypy is complaining that "InnerClass" is not defined. I've tried from __future__ import annotations, but that didn't help either.

Is there a better way to define this or is this potentially a bug in Mypy? Thanks!

[erictraut]

Mypy is correct to generate an error here. Pylint is probably just missing a check.

The InnerClass symbol is defined in an inner scope and has no meaning where you are referencing it. The quotes mean that forward references are allowed, but this symbol is not a forward reference.

If you want the type declaration to be visible outside of the function, you should declare it outside of the function, like this:

class MyClass:
    pass

def class_factory() -> type[MyClass]:
    return MyClass

[jodhus]

Funny enough, I normally don't do inner/nested classes. I should have stuck to my instincts.

Appreciate the insight. Thanks!