docs: 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,))