请帮我写一段在Carla中设置npc车辆，使其循环的（创建触发器）只从A点以速度50朝着B点运动的正确代码

好的，以下是在CARLA中设置NPC车辆并创建循环触发器的Python代码示例：

import carla
import random

# Connect to the CARLA server
client = carla.Client('localhost', 2000)
client.set_timeout(10.0)

# Get the world and map
world = client.get_world()
map = world.get_map()

# Define the start and end points of the NPC vehicle
start_point = carla.Location(x=-50, y=0, z=2)
end_point = carla.Location(x=50, y=0, z=2)

# Spawn the NPC vehicle
bp_lib = world.get_blueprint_library()
bp = random.choice(bp_lib.filter('vehicle.*'))
spawn_point = random.choice(map.get_spawn_points())
vehicle = world.spawn_actor(bp, spawn_point)

# Set the NPC vehicle's destination and maximum speed
vehicle.set_autopilot(True)
vehicle.set_target_location(end_point)
vehicle.set_max_speed(50)

# Create a trigger box at the start point
start_box = carla.TriggerBox(carla.Transform(start_point), carla.Vector3D(5, 5, 5))
start_trigger = world.spawn_actor(start_box)

# Create a trigger box at the end point
end_box = carla.TriggerBox(carla.Transform(end_point), carla.Vector3D(5, 5, 5))
end_trigger = world.spawn_actor(end_box)

# Define the function to be called when the NPC vehicle enters the start trigger
def on_start_trigger(other_actor):
    if other_actor == vehicle:
        vehicle.set_target_location(end_point)

# Define the function to be called when the NPC vehicle enters the end trigger
def on_end_trigger(other_actor):
    if other_actor == vehicle:
        vehicle.set_target_location(start_point)

# Attach the start and end trigger events to the trigger boxes
start_trigger.listen(lambda event: on_start_trigger(event.other_actor))
end_trigger.listen(lambda event: on_end_trigger(event.other_actor))

# Start the simulation loop
try:
    while True:
        world.tick()
finally:
    pass

这段代码将生成一个NPC车辆，使其在起点和终点之间循环移动。触发器箱在起点和终点处创建。当NPC车辆进入起点触发器时，将调用on_start_trigger函数，并将NPC车辆的目标位置设置为终点。当NPC车辆进入终点触发器时，将调用on_end_trigger函数，并将NPC车辆的目标位置设置为起点。这样，NPC车辆将在起点和终点之间循环移动。