Demo Launch

The use of ROS 2 launch files seems scattered. In this repository we demonstrate how to structure ROS 2 launch files as Mixins. This offers some advantages:

• Code completion (so to understand what nodes / arguments a package offers / needs)
• Flexible composition (mix and match)
• Importable (but launch files inclusion still possible)

  • Include launch file

    from launch.actions import IncludeLaunchDescription
    from launch.launch_description_sources import PythonLaunchDescriptionSource
    from launch.substitutions import PathJoinSubstitution
    from launch_ros.substitutions import FindPackageShare

  • Mixins

    from launch_mixins.demo_launch import TurtleSimMixin, HelloWorldMixin

How To

General Setup

For the general setup, do:

1. In package.xml, add

   <builtool_depend>ament_cmake_python</buildtool_depend>

2. In CMakeLists.txt, add

   find_package(ament_cmake_python REQUIRED)
   ...
   # install mixins
   ament_python_install_package(launch_mixins)

3. Put your Mixins into launch_mixins/demo_launch folder (or your desired name). Add launch_mixins/__init__.py and launch_mixins/demo_launch/__init__.py file. Replace demo_launch by your package name.

Create your Mixin

Create Mixin classes for your package, see mixins.py:

1. For each node, launch argument etc. create a static method
2. Prefix them with node_ for nodes and arg_ for arguments (this helps code completion)

Example Use

An example use is shown in the turtlesim_hello_world.launch.py launch file. You'll do things like

ld = LaunchDescription()

# add turtlesim
ld.add_action(TurtleSimMixin.arg_node_name())
ld.add_action(TurtleSimMixin.node_turtlesim())

But you might also keep references (for event handlers)

turtlesim_node = TurtleSimMixin.node_turtlesim()

You can also create new classes

class MyNewLaunch(HelloWorldMixin, TurtleSimMixin):
    pass

Code Completion Setup (VS Code)

For code completion extend the Python path:

1. In settings.json add

   {
       "python.envFile": "${workspaceFolder}/.env"
   }

2. In .env add (requires colcon build this package)

   PYTHONPATH=../../install/launch_mixins/local/lib/python3.10