Since Python 3.5 you may use typing module.
Quoting docs,
A type alias is defined by assigning the type to the alias:
Vector = List[float]
To learn more about enforcing types in Python you may want to get familiar with PEPs: PEP483 and PEP484.
Python historically was using duck-typing instead of strong typing and hadn’t built-in way of declaring types before 3.5 release.