docs: def _check_and_assign_normalization_members(self, normalization_ctor,
                                                normalization_kwargs):
      """Checks that the normalization constructor is callable."""
      if isinstance(normalization_ctor, six.string_types):
        normalization_ctor = util.parse_string_to_constructor(normalization_ctor)
      if normalization_ctor is not None and not callable(normalization_ctor):
        raise ValueError(
            "normalization_ctor must be a callable or a string that specifies "
            "a callable, got {}.".format(normalization_ctor))
      self._normalization_ctor = normalization_ctor
      self._normalization_kwargs = normalization_kwargs