In the following simple ROS2 Python Node I am just trying to change a parameter from the CLI and print it within the Node to the terminal.

As soon as I use ros2 param set and change the value, I am stuck in sleep() function of the while loop.

I am using Ubuntu 18.04 in a VM with ROS2 Eloquent installed.

#!/usr/bin/env python3

import rclpy

def main():
    rclpy.init()
    myfirstnode = rclpy.create_node('my_param_node')
    myfirstnode.declare_parameter('my_param', 13)
    rate = myfirstnode.create_rate(1.0) #define a rate of 1 Hz
    while rclpy.ok():
        try:
            print('===1===')
            rclpy.spin_once(myfirstnode)
            print('===2===')
        except KeyboardInterrupt:
            pass
        print('===3===')
        print(myfirstnode.get_parameter('my_param').value)
        print('===4===')
        rate.sleep()
        print('===5===')
    myfirstnode.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

I set the value of my_param to 42 and the terminal output looks like that:

===1===
===2===
===3===
13
===4===
===5===
===1===
===2===
===3===
13
===4===
===5===
===1===
===2===
===3===
42
===4===

And then it stops.