### ROS Python 发布与订阅示例 #### 创建ROS节点 为了创建一个能够发布和订阅消息的Python脚本，在ROS环境中，首先需要初始化一个新的ROS节点。这可以通过`rospy.init_node()`函数来完成[^3]。 ```python import rospy from std_msgs.msg import String def talker(): pub = rospy.Publisher('chatter', String, queue_size=10) rospy.init_node('talker', anonymous=True) rate = rospy.Rate(10) # 10hz while not rospy.is_shutdown(): hello_str = "hello world %s" % rospy.get_time() rospy.loginfo(hello_str) pub.publish(hello_str) rate.sleep() if __name__ == '__main__': try: talker() except rospy.ROSInterruptException: pass ``` 这段代码展示了如何设置一个简单的发布者节点，它会每隔一秒向名为`'chatter'`的话题发送一条字符串消息[^1]。 #### 编写订阅者的Python程序 对于想要接收来自特定话题的消息的应用来说，则需编写相应的订阅者逻辑。下面是一个监听上述发布的简单例子： ```python def callback(data): rospy.loginfo(rospy.get_caller_id() + "I heard %s", data.data) def listener(): # In ROS, nodes are uniquely named. If two nodes with the same # name are launched, the previous one is kicked off. The # anonymous=True flag means that rospy will choose a unique # name for our 'listener' node so that multiple listeners can # run simultaneously. rospy.init_node('listener', anonymous=True) rospy.Subscriber("chatter", String, callback) # spin() simply keeps python from exiting until this node is stopped rospy.spin() if __name__ == '__main__': listener() ``` 此段代码定义了一个回调函数用于处理接收到的数据，并注册了这个函数作为当有新数据到达时要执行的操作。每当新的消息被传送到指定的主题上时就会触发一次回调函数调用。 #### 使用Turtlesim实例化操作 如果希望看到更具体的案例，比如控制模拟环境中的海龟移动，那么可以参照如下方式修改上面的例子以适应`turtlesim/Twist`类型的消息格式并实际操控虚拟角色的动作。 ```python #!/usr/bin/env python import rospy from geometry_msgs.msg import Twist def move_turtle(linear_speed, angular_speed): cmd_vel_topic = '/turtle1/cmd_vel' velocity_publisher = rospy.Publisher(cmd_vel_topic, Twist, queue_size=10) vel_msg = Twist() vel_msg.linear.x = linear_speed vel_msg.angular.z = angular_speed loop_rate = rospy.Rate(10) while not rospy.is_shutdown(): rospy.loginfo("Moving turtle") velocity_publisher.publish(vel_msg) loop_rate.sleep() if __name__ == "__main__": try: rospy.init_node('move_turtle') move_turtle(float(input("Set your linear speed:")), float(input("Set your angular speed:"))) except rospy.ROSInterruptException as e: print(e) ``` 在这个版本里，用户可以根据提示输入线速度和角速度参数从而改变乌龟前进的方向以及旋转的速度。