> SupportsIndex makes it so that, if you have a value that's not a Python int but can be implicitly and losslessly converted to one

Just to be clear for folks who care more about the general python around this: any class that has a method __index__ that returns an int can be used as an index for array access. e.g:

    class FetchIndex:
        def __index__(self):
            return int(requests.get("https://indextolookup.com").text.strip())
            

    a = ["no", "lol", "wow"]
    print(a[FetchIndex()])

The builtin `int` also has a __index__ method that returns itself.

Dunders are part of what makes typing in python so hard.