model.py 文件源码

def get_entity(
            self, entity_type, entity_id, history_index=-1, connected=True):
        """Return an object instance for the given entity_type and id.

        By default the object state matches the most recent state from
        Juju. To get an instance of the object in an older state, pass
        history_index, an index into the history deque for the entity.

        """

        if history_index < 0 and history_index != -1:
            history_index += len(self.entity_history(entity_type, entity_id))
            if history_index < 0:
                return None

        try:
            self.entity_data(entity_type, entity_id, history_index)
        except IndexError:
            return None

        entity_class = get_entity_class(entity_type)
        return entity_class(
            entity_id, self.model, history_index=history_index,
            connected=connected)