Hi There! I’m new to ROS2 and I’m struggling in coding a node acting as both subscriber and publisher to exchange data with other nodes. I’ve tried to modify the python code in the ROS2 Tutorial but I still don't get how to make it work. Any suggestions?

Below I'm attaching the modified Publisher and Subscriber codes.

Many thanks! Alex

Publisher

import rclpy from rclpy.node import Node

from std_msgs.msg import String

class MinimalPublisher(Node):

def __init__(self):
    super().__init__('minimal_publisher')
    self.publisher_ = self.create_publisher(String, 'topic', 10)
    timer_period = 0.5  # seconds
    self.timer = self.create_timer(timer_period, self.timer_callback)
    self.i = 0

    self.subscription = self.create_subscription(
        String,
        'return',
        self.listener_callback,
        10)
    self.subscription

def listener_callback( self, msg):
    self.get_logger().info(' Returned msg: I heard: "%s"' % msg.data)

def timer_callback(self):
    msg = String()
    msg.data = 'Hello World: %d' % self.i
    self.publisher_.publish(msg)
    self.get_logger().info('Publishing: "%s"' % msg.data)
    self.i += 1

def main(args=None): rclpy.init(args=args)

minimal_publisher = MinimalPublisher()

rclpy.spin(minimal_publisher)

minimal_publisher.destroy_node()
rclpy.shutdown()

if __name__ == '__main__': main()

Subscriber

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

    self.publisher_ = self.create_publisher( String, 'return', 10)
    time_period = 0.5
    self_timer = self_create_timer(time_period, self.timer_callback)
    self.i = 0

def listener_callback(self, msg):
    self.get_logger().info('I heard: "%s"' % msg.data)

def timer_callback(self)
  msg = String()
  msg.data = 'Received' %d ' % self.i
  self.publisher_.publish(msg)
  self.get_logger().info('Publishing return msg: "%s"' % msg.data)
  self.i += 1

def main(args=None): rclpy.init(args=args)

minimal_subscriber = MinimalSubscriber()

rclpy.spin(minimal_subscriber)

minimal_subscriber.destroy_node()
rclpy.shutdown()

if __name__ == '__main__': main()