Method foo

Lib/test/test_typing.py:7975–7979

(a: A)

        A = Optional[Type[BaseException]]

        def foo(a: A) -> Optional[BaseException]:
            if a is None:
                return None
            else:
                return a()

        self.assertIsInstance(foo(KeyboardInterrupt), KeyboardInterrupt)
        self.assertIsNone(foo(None))