How to create a simple Python node

1. docker-compose exec dev bash

2. cd src

3. ros2 pkg create my_py_pkg --build-type ament_python --dependencies rclpy

4. Create a Python file: touch my_py_pkg/my_py_pkg/my_first_node.py

5. Edit the file and add:

   #!/usr/bin/env python3
   import rclpy
   from rclpy.node import Node
   
   
   def main(args=None):
       rclpy.init(args=args)
       node = Node('py_test')
       node.get_logger().info('Hello ROS2')
       rclpy.spin(node)
       rclpy.shutdown()
   
   
   if __name__ == '__main__':
       main()

6. Make the file executable: chmod +x the_python_file.py. Then you can execute by running ./the_python_file.py

7. Add your node to src/my_py_pkg/setup.py

   entry_points={
       'console_scripts': [
           'py_node = my_py_pkg.my_first_node:main' # <-- this line
       ],
   },

8. Go to the root of your workspace: cd /ros2_ws

9. Build your package: colcon build --packages-select my_py_pkg --symlink-install

10. Source again: source ~/.bashrc

11. Run your node manually: ./install/my_py_pkg/lib/my_py_pkg/py_node

12. Run your node through ROS2 commands (source ~/.bashrc again if necessary): ros2 run my_py_pkg py_node