How to load custom maps for town or maps that come with Carla?

[xuarehere]

When I run the code below, there is an error and it cannot load town03 or other maps

customized_highway_env/envs/common/carla_utils.py

    def set_up_carla(self):
        self.client = carla.Client('localhost', 2000)
        self.client.set_timeout(2.0)
        self.world = self.client.load_world('zz2')