Python should use different types to represent datetimes with a timezone and those without.

    class Datetime:
        pass

    class NaiveDatetime:
        pass

That way you can annotate functions properly.

    def timezone(datetime: Datetime) -> ...:

This is how Elixir does it. So much easier to understand as a newcomer.

https://hexdocs.pm/elixir/DateTime.html https://hexdocs.pm/elixir/NaiveDateTime.html