ROS2 Python Launch - Basic Node Launch

🧠 Concept: Launch Files

Launch files let you start multiple nodes at once with a single command. Instead of opening 5 terminals and running ros2 run in each, you write one Python launch file.

Minimal structure:

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='my_package',
            executable='my_node',
            name='my_node_name',    # optional — overrides the node's internal name
            output='screen',        # print logs to terminal
        ),
    ])

Key: The function MUST be named generate_launch_description() — ROS2 looks for this exact name.

Problem Statement

Create a basic Launch file to start a single ROS2 node. This introduces the LaunchDescription and Node action.

Requirements

• Create a function generate_launch_description
• Launch package: demo_nodes_cpp, executable: talker
• Set parameter: param1 to "value1"
• Remap topic: /chatter to /my_chatter
• Note: The test uses mocks, so these packages don't need to physically exist.

Input/Output Format

Output:

• Return a LaunchDescription object

⚠️ Common Pitfalls

• Forgetting to import Node from launch_ros.actions.
• Remappings are a list of tuples: [('/old', '/new')].

📚 Helpful Resources

• ROS2 Launch Tutorials