Currently, @typing.final is implemented as an identity function, which makes it impossible for type checkers that look at runtime objects to support it.

I propose that we implement it as something like:

    def final(f):
        try:
            f.__final__ = True
        except AttributeError:
            pass  # in case it is used on an object that doesn't support setting attributes
        return f

I will submit a PR implementing this idea.