crash_mypy.py

import dataclasses


@dataclasses.dataclass
class MyClass:
    a: dataclasses.InitVar[int]
    _a: int = dataclasses.field(init=False)

    def __post_init__(self, a: int) -> None:
        self._a = a


@dataclasses.dataclass
class MySubClass(MyClass):
    b: int = dataclasses.field(init=False)

    def __post_init__(self, a: int) -> None:
        super().__post_init__(a)
        self.b = a + 1


@dataclasses.dataclass(init=False)
class MyFinalClass(MySubClass):
    c: int

    def __init__(self, a: int, c: int) -> None:
        super().__init__(a)
        self.c = c + self.b


assert MyClass(100)._a == 100
assert MySubClass(100)._a == 100
assert MySubClass(100).b == 101
assert MyFinalClass(100, 50)._a == 100
assert MyFinalClass(100, 50).b == 101
assert MyFinalClass(100, 50).c == 151