Writing Python Publisher 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 approach

Below is an example of each approach to write a Python node publishing “Hello World”. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclpy/topics/minimal_publisher/examples_rclpy_minimal_publisher

Old-school approach:

from time import sleep

import rclpy

from std_msgs.msg import String

# We do not recommend this style as ROS 2 provides timers for this purpose,
# and it is recommended that all nodes call a variation of spin.
# This example is only included for completeness because it is similar to examples in ROS 1.
# For periodic publication please see the other examples using timers.


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

    node = rclpy.create_node('minimal_publisher')

    publisher = node.create_publisher(String, 'topic', 10)

    msg = String()

    i = 0
    while rclpy.ok():
        msg.data = 'Hello World: %d' % i
        i += 1
        node.get_logger().info('Publishing: "%s"' % msg.data)
        publisher.publish(msg)
        sleep(0.5)  # seconds

    # 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()

Object-oriented (member-function) approach:

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

    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)

    # Destroy the node explicitly
    # (optional - otherwise it will be done automatically
    # when the garbage collector destroys the node object)
    minimal_publisher.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

Local function approach:

import rclpy

from std_msgs.msg import String


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

    node = rclpy.create_node('minimal_publisher')
    publisher = node.create_publisher(String, 'topic', 10)

    msg = String()
    i = 0

    def timer_callback():
        nonlocal i
        msg.data = 'Hello World: %d' % i
        i += 1
        node.get_logger().info('Publishing: "%s"' % msg.data)
        publisher.publish(msg)

    timer_period = 0.5  # seconds
    timer = node.create_timer(timer_period, timer_callback)

    rclpy.spin(node)

    # Destroy the timer attached to the node explicitly
    # (optional - otherwise it will be done automatically
    # when the garbage collector destroys the node object)
    node.destroy_timer(timer)
    node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()