| class P(Protocol): | |
| x: int | |
| class C: | |
| def initialize(self) -> None: | |
| self.x = 0 | |
| c = C() | |
| isinstance(c, P) # False | |
| c.initialize() | |
| isinstance(c, P) # True | |
| def f(x: Union[P, int]) -> None: | |
| if isinstance(x, P): | |
| # Static type of x is P here. | |
| ... | |
| else: | |
| # Static type of x is int, but can be other type at runtime... | |
| print(x + 1) | |
| f(C()) # ...causing a TypeError. | |