code: def _validate_contains(self, expected_values, field, value):
          
          if not isinstance(value, Iterable):
              return
  
          if not isinstance(expected_values, Iterable) or isinstance(
              expected_values, _str_type
          ):
              expected_values = set((expected_values,))
          else:
              expected_values = set(expected_values)
  
          missing_values = expected_values - set(value)
          if missing_values:
              self._error(field, errors.MISSING_MEMBERS, missing_values)
docs: {'empty': False }