Without a def

When the overloads already exist as a plain mapping from type to callable, Function.from_mapping builds a dispatched function from that mapping directly, with no def needed for any of the overloads. A tuple key gives one positional hint per element:

>>> from bagof.dispatchers import Function
>>> size = Function.from_mapping({(int,): abs, (str,): len}, name="size")
>>> size(-3)
3
>>> size("abcd")
4

Signatures a plain tuple cannot spell

A plain tuple of hints can only describe ordinary positional parameters. For a signature shape it cannot spell, such as positional-only parameters, *args, or keyword-only parameters, pass a Signature as the key instead:

>>> from bagof.dispatchers import Function, Signature
>>> total = Function.from_mapping({Signature.from_hints(int, int): lambda a, b: a + b})
>>> total(2, 3)
5