Previously, Python required using the typing module to provide tools for describing such types. As of Python 3.9, they can be done natively in Python: dict_of_users: dict ...

Python’s typing module, used to annotate code with type information, lets you describe the types of a callable (e.g., a function). But that type information can’t be propagated across callables.

Given that, as shown above, functions are of type function, perhaps you can use that. But function isn't actually a recognized name in Python. Instead, you'll need to use the typing module, which ...

One of the most popular answers is a system known as mypy, which takes advantage of Python 3's type annotations for its own purposes. ... I've grabbed Sequence from the typing module, which includes ...