code: def _validate_allowed(self, allowed_values, field, value):
          
          if isinstance(value, Iterable) and not isinstance(value, _str_type):
              unallowed = set(value) - set(allowed_values)
              if unallowed:
                  self._error(field, errors.UNALLOWED_VALUES, list(unallowed))
          else:
              if value not in allowed_values:
                  self._error(field, errors.UNALLOWED_VALUE, value)
docs: {'type': 'list'}