useless-mypy.py

#!/usr/bin/env python3

from typing import Any

class Foo:
    def __init__(self, a: str):
        self.a: str = a

    def bark(self) -> str:
        # can only call upper on str's
        return self.a.upper()

foo: Any = 3
reveal_type(foo)  # Any

f = Foo(foo)
reveal_type(f.a)  # str, even though it isn't

f.bark()  # Runtime exception