def __init__(self, init_observations):
        """
        The real init is happened in self.init(), in which super().__init__() will be called
        """
        super(VehicleAgentManager, self).__init__(init_observations)
        # For multi-agent env, None values is updated in init()
        self._allow_respawn = None
        self._delay_done = None
        self._infinite_agents = None

        self._dying_objects = {}  # BaseVehicles which will be recycled after the delay_done time
        self._agents_finished_this_frame = dict()  # for observation space
        self.next_agent_count = 0

        The real init is happened in self.init(), in which super().__init__() will be called
        
metadrive/manager/agent_manager.py