def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def update_snapshot(self, snapshot_id, **kwargs):
        """Updates a snapshot."""
        put_body = json.dumps({'snapshot': kwargs})
        resp, body = self.put('snapshots/%s' % snapshot_id, put_body)
        body = json.loads(body)
        return resp, body['snapshot']