You picked a poor example for `mean` because there's a very easy answer: collections.abc.Sequence – typing.Sequence in earlier versions – an object that support

You picked a poor example for `mean` because there's a very easy answer: collections.abc.Sequence – typing.Sequence in earlier versions – an object that supports __getitem__ and __len__. You can check the collections.abc documentation[1] for the available protocols; you might be surprised about how much they cover already. I often use Sequence/Iterable or Mapping as parameter types instead of concrete types like list or dict. > I feel like a lot of people who want static typing everywhere want it as training wheels for other devs they don't trust to make the right judgement calls. Now, I want it because it makes my life a lot easier. It finds many classes of errors before runtime and improves auto-completion in my editor. For most programs, it's not a lot of effort. The frustrating part is interfacing with untyped libraries while using strict type-checking, but thankfully, more and more libraries are adopting typing. The type system itself is fine: most things you want to express are doable, but it's not at the same level of complexity as Typescript. It's certainly a better type system than Go's for example. [1] https://docs.python.org/3/library/collections.abc.html https://docs.python.org/3/library/collections.abc.html