I like the term "type hint" because that really is exactly what they are. Typecheckers like mypy are (1) optional, and (2) are only as good as the type hints t

I like the term "type hint" because that really is exactly what they are. Typecheckers like mypy are (1) optional, and (2) are only as good as the type hints themselves. Unlike with a language that's actually statically typed, the relation of the type annotations to the actual types of the data operates largely on the honor system, so the type checking is more a validation of internal consistency than full-on static type safety. Which is fine, and well within Python's "We're all adults here" ethos. It's just that it's still not anywhere near the level of rigor you get out of the type checker in a language like OCaml.