Writing Python Subscriber in ROS2
There are three ways to to write a Python publisher in ROS2, namely:
- Old-school approach
- Object-oriented (member-function) approach
- Local function (lambda) approach
Below is an example of each approach to write a Python node listening to “Hello World” stream. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclpy/topics/minimal_subscriber/examples_rclpy_minimal_subscriber
Old-school approach:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 |
import rclpy from std_msgs.msg import String g_node = None def chatter_callback(msg): global g_node g_node.get_logger().info( 'I heard: "%s"' % msg.data) def main(args=None): global g_node rclpy.init(args=args) g_node = rclpy.create_node('minimal_subscriber') subscription = g_node.create_subscription(String, 'topic', chatter_callback, 10) subscription # prevent unused variable warning while rclpy.ok(): rclpy.spin_once(g_node) # Destroy the node explicitly # (optional - otherwise it will be done automatically # when the garbage collector destroys the node object) g_node.destroy_node() rclpy.shutdown() if __name__ == '__main__': main() |
Object-oriented (member-function) approach:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 |
import rclpy from rclpy.node import Node from std_msgs.msg import String class MinimalSubscriber(Node): def __init__(self): super().__init__('minimal_subscriber') self.subscription = self.create_subscription( String, 'topic', self.listener_callback, 10) self.subscription # prevent unused variable warning def listener_callback(self, msg): self.get_logger().info('I heard: "%s"' % msg.data) def main(args=None): rclpy.init(args=args) minimal_subscriber = MinimalSubscriber() rclpy.spin(minimal_subscriber) # Destroy the node explicitly # (optional - otherwise it will be done automatically # when the garbage collector destroys the node object) minimal_subscriber.destroy_node() rclpy.shutdown() if __name__ == '__main__': main() |
Local function (lambda) approach:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 |
import rclpy from std_msgs.msg import String def main(args=None): rclpy.init(args=args) node = rclpy.create_node('minimal_subscriber') subscription = node.create_subscription( String, 'topic', lambda msg: node.get_logger().info('I heard: "%s"' % msg.data), 10) subscription # prevent unused variable warning rclpy.spin(node) # Destroy the node explicitly # (optional - otherwise it will be done automatically # when the garbage collector destroys the node object) node.destroy_node() rclpy.shutdown() if __name__ == '__main__': main() |