🔒 MyPy errors calling a classmethod from a classmethod

[storm ginkgo]

Sample code:

from typing import Self


class Foo:
    a: int

    def __init__(self, a: int):
        self.a = a

    @classmethod
    def m1(cls) -> Self:
        return Foo.m2()

    @classmethod
    def m2(cls) -> Self:
        return cls(100)


print(f"m2: {Foo.m2().a}")
print(f"m1: {Foo.m1().a}")

The code seems to work fine, both m1 and m2 print 100. However, MyPY doesn't seem to know that Foo and Self are the same type:

a.py:12: error: Incompatible return value type (got "Foo", expected "Self")  [return-value]
Found 1 error in 1 file (checked 1 source file)

What is the proper way to type hint this? Or is there a better way to write it?

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@storm ginkgo

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[storm ginkgo]

Discovered a solution at https://github.com/python/mypy/issues/16558: Self is a distinct type, but cls has the type Self, so this is accepted:

    @classmethod
    def m1(cls) -> Self:
        return type(cls).m2()

Seems a bit hacky but it works

!close

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