def METHOD_NAME(
    arg: Iterable[Any],
    cls: type,
    msg: str = "Expected a list of {name}, not {arg!r}",
) -> None:
    _check_iterable(arg, msg, name=cls.__name__)
    if not all(isinstance(instance, cls) for instance in arg):
        raise exceptions.ValidationError(msg.format(arg=arg, name=cls.__name__))