def reward_function(self, object_id: str) -> Tuple[float, Dict]:
        """
        Override this func to get a new reward function
        :param object_id: name of this object
        :return: reward, reward info
        """
        self.logger.warning("Reward function is not implemented. Return reward = 0", extra={"log_once": True})
        return 0, {}

        Override this func to get a new reward function
        :param object_id: name of this object
        :return: reward, reward info
        
metadrive/envs/base_env.py