How to publish a msg one time using ros2 in python

General Support
2

Hello @mbzuaimbzirc,

one posible way is to apply a transient local QOS setting profile to your publisher.

For instance using this minimal publisher example taken from ROS Answers.
Source: ros2 latching - ROS Answers: Open Source Q&A Forum

#!/usr/bin/env python

import rclpy
from rclpy.node import Node
from rclpy.qos import QoSProfile, QoSDurabilityPolicy
from std_msgs.msg import String


class Latching(Node):

    def __init__(self):
        super().__init__('latching')
        latching_qos = QoSProfile(depth=1, durability=DurabilityPolicy.TRANSIENT_LOCAL)
        pub = self.create_publisher(String, 'foo', qos_profile=latching_qos)
        msg = String(data='test')
        pub.publish(msg)


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

    try:
        rclpy.spin(node)
    except KeyboardInterrupt:
        node.get_logger().info("Ctrl-C detected, shutting down")
    finally:
        node.destroy_node()
        rclpy.shutdown()


if __name__ == '__main__':
    main()

Cheers,

Roberto