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ROS2 在 Python 编程中引入了一些新的概念和 API，这些变化使得代码更加模块化和易于维护。特别是 rclpy 库提供了更丰富的功能和更好的错误处理机制，同时支持异步编程模型。如果你已经熟悉 ROS1 的 Python 编程，这些变化应该不会太难适应。

一、初始化和关闭节点

ROS1:

import rospydef main():rospy.init_node('my_node', anonymous=True)# 节点逻辑rospy.spin()if __name__ == '__main__':main()

ROS2:

import rclpy
from rclpy.node import Nodeclass MyNode(Node):def __init__(self):super().__init__('my_node')# 节点逻辑def main(args=None):rclpy.init(args=args)node = MyNode()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

二、发布者

ROS1:

import rospy
from std_msgs.msg import Stringdef talker():pub = rospy.Publisher('chatter', String, queue_size=10)rospy.init_node('talker', anonymous=True)rate = rospy.Rate(10)  # 10 Hzwhile 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

ROS2:

import rclpy
from rclpy.node import Node
from std_msgs.msg import Stringclass Talker(Node):def __init__(self):super().__init__('talker')self.publisher_ = self.create_publisher(String, 'chatter', 10)timer_period = 1  # secondsself.timer = self.create_timer(timer_period, self.timer_callback)def timer_callback(self):msg = String()msg.data = f'Hello World {self.get_clock().now().nanoseconds // 1000000}'self.get_logger().info(f'Publishing: "{msg.data}"')self.publisher_.publish(msg)def main(args=None):rclpy.init(args=args)node = Talker()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

三、订阅者

ROS1:

import rospy
from std_msgs.msg import Stringdef callback(data):rospy.loginfo(rospy.get_caller_id() + " I heard %s", data.data)def listener():rospy.init_node('listener', anonymous=True)rospy.Subscriber('chatter', String, callback)rospy.spin()if __name__ == '__main__':listener()

ROS2:

import rclpy
from rclpy.node import Node
from std_msgs.msg import Stringclass Listener(Node):def __init__(self):super().__init__('listener')self.subscription = self.create_subscription(String, 'chatter', self.listener_callback, 10)self.subscription  # prevent unused variable warningdef listener_callback(self, msg):self.get_logger().info(f'I heard: "{msg.data}"')def main(args=None):rclpy.init(args=args)node = Listener()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

四、服务端

ROS1:

import rospy
from std_srvs.srv import AddTwoIntsdef handle_add_two_ints(req):rospy.loginfo(f"Returning [{req.a} + {req.b} = {req.a + req.b}]")return AddTwoIntsResponse(req.a + req.b)def add_two_ints_server():rospy.init_node('add_two_ints_server')s = rospy.Service('add_two_ints', AddTwoInts, handle_add_two_ints)rospy.spin()if __name__ == "__main__":add_two_ints_server()

ROS2:

import rclpy
from rclpy.node import Node
from example_interfaces.srv import AddTwoIntsclass AddTwoIntsService(Node):def __init__(self):super().__init__('add_two_ints_server')self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)def add_two_ints_callback(self, request, response):response.sum = request.a + request.bself.get_logger().info(f'Returning [{request.a} + {request.b} = {response.sum}]')return responsedef main(args=None):rclpy.init(args=args)node = AddTwoIntsService()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

五、客户端

ROS1:

import rospy
from std_srvs.srv import AddTwoIntsdef add_two_ints_client(x, y):rospy.wait_for_service('add_two_ints')try:add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)resp1 = add_two_ints(x, y)return resp1.sumexcept rospy.ServiceException as e:print(f"Service call failed: {e}")if __name__ == "__main__":rospy.init_node('add_two_ints_client')x = 1y = 2print(f"Requesting {x}+{y}")print(f"{x} + {y} = {add_two_ints_client(x, y)}")

ROS2:

import rclpy
from rclpy.node import Node
from example_interfaces.srv import AddTwoIntsclass AddTwoIntsClient(Node):def __init__(self):super().__init__('add_two_ints_client')self.cli = self.create_client(AddTwoInts, 'add_two_ints')while not self.cli.wait_for_service(timeout_sec=1.0):self.get_logger().info('service not available, waiting again...')self.req = AddTwoInts.Request()def send_request(self, a, b):self.req.a = aself.req.b = bself.future = self.cli.call_async(self.req)def main(args=None):rclpy.init(args=args)node = AddTwoIntsClient()node.send_request(16, 2)while rclpy.ok():rclpy.spin_once(node)if node.future.done():try:response = node.future.result()except Exception as e:node.get_logger().info(f'Service call failed {e}')else:node.get_logger().info(f'Result of add_two_ints: {response.sum}')breaknode.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

六、参数管理

ROS1:

在ROS1中，参数管理是通过全局参数服务器来实现的。

import rospydef main():rospy.init_node('my_node', anonymous=True)# 获取参数param_value = rospy.get_param('param_name', 'default_value')rospy.loginfo(f"Parameter value: {param_value}")# 设置参数rospy.set_param('param_name', 'new_value')if __name__ == '__main__':main()

ROS2:

在ROS2中，参数管理更加灵活，支持类型安全的参数接口和参数描述符。

import rclpy
from rclpy.node import Nodeclass MyNode(Node):def __init__(self):super().__init__('my_node')# 获取参数param_value = self.get_parameter('param_name').get_parameter_value().string_valueself.get_logger().info(f"Parameter value: {param_value}")# 设置参数self.set_parameters([rclpy.parameter.Parameter('param_name', rclpy.Parameter.Type.STRING, 'new_value')])def main(args=None):rclpy.init(args=args)node = MyNode()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

七、日志记录

ROS1:

在ROS1中，日志记录使用 rospy 提供的函数。

import rospydef main():rospy.init_node('my_node', anonymous=True)rospy.loginfo("This is an info message.")rospy.logwarn("This is a warning message.")rospy.logerr("This is an error message.")rospy.logfatal("This is a fatal message.") if __name__ == '__main__':main()

ROS2:

在ROS2中，日志记录使用 rclpy 提供的函数。

import rclpy
from rclpy.node import Nodeclass MyNode(Node):def __init__(self):super().__init__('my_node')self.get_logger().info("This is an info message.")self.get_logger().warning("This is a warning message.")self.get_logger().error("This is an error message.")self.get_logger().fatal("This is a fatal message.")def main(args=None):rclpy.init(args=args)node = MyNode()rclpy.spin(node)node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

八、生命周期管理

ROS1:

ROS1没有内置的生命周期管理功能，通常需要开发者自己实现节点的生命周期管理。

ROS2:

ROS2引入了生命周期管理，允许更精细地控制节点的启动和停止过程。

import rclpy
from rclpy.lifecycle import Node, State, TransitionCallbackReturn
from rclpy.node import Node as BaseNodeclass LifecycleNode(Node):def __init__(self):super().__init__('lifecycle_node')def on_configure(self, state: State) -> TransitionCallbackReturn:self.get_logger().info('on_configure() is called.')return TransitionCallbackReturn.SUCCESSdef on_activate(self, state: State) -> TransitionCallbackReturn:self.get_logger().info('on_activate() is called.')return TransitionCallbackReturn.SUCCESSdef on_deactivate(self, state: State) -> TransitionCallbackReturn:self.get_logger().info('on_deactivate() is called.')return TransitionCallbackReturn.SUCCESSdef on_cleanup(self, state: State) -> TransitionCallbackReturn:self.get_logger().info('on_cleanup() is called.')return TransitionCallbackReturn.SUCCESSdef on_shutdown(self, state: State) -> TransitionCallbackReturn:self.get_logger().info('on_shutdown() is called.')return TransitionCallbackReturn.SUCCESSdef main(args=None):rclpy.init(args=args)node = LifecycleNode()executor = rclpy.executors.SingleThreadedExecutor()executor.add_node(node)try:executor.spin()except KeyboardInterrupt:passnode.on_shutdown(State(id=9, label='unconfigured'))node.destroy_node()rclpy.shutdown()if __name__ == '__main__':main()

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