@classmethod<EOL><INDENT>def key_for_entity_group(cls, key):<DEDENT>
return model.Key(cls.KIND_NAME, cls.ID, parent=key.root())<EOL>
Return the key for the entity group containing key.

        Args:
          key: a key for an entity group whose __entity_group__ key you want.

        Returns:
          The __entity_group__ key for the entity group containing key.