2.3 Building ROS 2 packages with Python

Creating ROS 2 Packages in Python

Overview

This module covers how to create ROS 2 Python packages, structure nodes, and use topics, services, and actions.

Workflow Diagram

flowchart TD
    A[Create Workspace] --> B[Create ROS 2 Package]
    B --> C[Write Python Nodes]
    C --> D[Setup setup.py & package.xml]
    D --> E[Build Workspace]
    E --> F[Source Overlay]
    F --> G[Run Nodes]

Steps to Create a ROS 2 Python Package

1. Create workspace:

   mkdir -p ~/ros2_ws/src
   cd ~/ros2_ws

2. Create package:

   ros2 pkg create --build-type ament_python my_python_pkg

3. Write node:

   import rclpy
   from rclpy.node import Node
   
   class MinimalNode(Node):
       def __init__(self):
           super().__init__('minimal_node')
           self.get_logger().info("Node Started")
   
   def main():
       rclpy.init()
       node = MinimalNode()
       rclpy.spin(node)
       node.destroy_node()
       rclpy.shutdown()
   
   if __name__ == "__main__":
       main()

4. Update setup.py and package.xml.

5. Build:

   colcon build

6. Source:

   source install/setup.bash

7. Run:

   ros2 run my_python_pkg minimal_node

Self‑Assignment

1. Create your own custom ROS 2 Python package.
2. Add two nodes communicating via a topic.
3. Add parameters to your node.
4. Document your package folder structure.
5. Try running nodes with remapping.

MCQs

1. ROS 2 Python packages use which build type? a) ament_cmake
   b) catkin
   c) ament_python
   d) bazel
2. The command to build a workspace is: a) ros2 build
   b) colcon build
   c) build_ros2
   d) rosbuild
3. Which file defines dependencies? a) setup.cfg
   b) node.py
   c) package.xml
   d) build.xml
4. Which function starts the ROS 2 client library? a) rclpy.run()
   b) rclpy.start()
   c) rclpy.init()
   d) rclpy.begin()
5. A ROS 2 node is: a) A sensor
   b) A running executable
   c) A folder
   d) A virtual machine