Read a Python Launch Description

A basic ROS 2 Python launch file usually returns a LaunchDescription containing actions.

Create a scratch example and read it before running it:

from launch import LaunchDescription
from launch_ros.actions import Node


def generate_launch_description():
    return LaunchDescription([
        Node(
            package='robotnix_pubsub',
            executable='talker',
            name='course_talker',
            output='screen',
        ),
        Node(
            package='robotnix_pubsub',
            executable='listener',
            name='course_listener',
            output='screen',
        ),
    ])

Read one Node action

package='robotnix_pubsub'

selects the package.

executable='talker'

selects the installed executable entry point.

name='course_talker'

sets the runtime node name.

output='screen'

makes process output visible in the launch terminal.

Prediction

Before launching, predict:

nodes visible:
topic visible:
which process prints publisher logs:
which process prints subscriber logs:

Checkpoint

Explain why the launch file does not replace talker.py or listener.py.