I managed to find type hints affecting runtime behavior in functools.register. https://docs.python.org/3/library/functools.html?highlight=functools#functools.si

I managed to find type hints affecting runtime behavior in functools.register. https://docs.python.org/3/library/functools.html?highlight=functools#functools.singledispatch https://docs.python.org/3/library/functools.html?highlight=f... > To add overloaded implementations to the function, use the register() attribute of the generic function, which can be used as a decorator. For functions annotated with types, the decorator will infer the type of the first argument automatically: That appears to be the only other case.