Return the parameters necessary to check type boundaries.

        Args:
            args: A tuple with two parameters: a type, and a slice representing
                the minimum and maximum lengths allowed for values of that
                type.

        Returns:
            A tuple with three parameters: a type, a slice, and the len
            function.

def _get_args(cls, args):
        # type: (tuple) -> Tuple[type, slice, Callable]
        """Return the parameters necessary to check type boundaries.

        Args:
            args: A tuple with two parameters: a type, and a slice representing
                the minimum and maximum lengths allowed for values of that
                type.

        Returns:
            A tuple with three parameters: a type, a slice, and the len
            function.
        """
        if not isinstance(args, tuple) or not len(args) == 2:
            raise TypeError(
                "{}[...] takes exactly two arguments.".format(cls.__name__)
            )
        return super(_LengthBoundedMeta, cls)._get_args(args + (len,))