Why does mypy say I have too many arguments

Question

I've got a class which has a method that creates instances of the class.

class Bar:
    @classmethod
    def create(cls, foo: int):
        return cls(foo)

    def __init__(self, foo: int) -> None:
        pass

When I run mypy against it, it says mypytest.py:4: error: Too many arguments for "Bar"

It seems like a bug to me, because this works fine

class Bar:
    @classmethod
    def create(cls, foo):
        return cls(foo)

    def __init__(self, foo: int) -> None:
        pass

I don't understand why a class method which defines the type of a parameter should break the creation of an instance. Am I missing something?

Answer 1

The answer is simple, just place the __init__ method first. For example this works fine:

class Bar:
    def __init__(self, foo: int) -> None:
        pass

    @classmethod
    def create(cls, foo: int):
        return cls(foo)

For some technical reasons, mypy currently behaves unexpectedly in some corner cases if __init__ (or __new__) is not the first method in the class definition. I think I have already seen a similar problem, but can't find an issue on mypy tracker.