Writing a topic subscriber

To continue improving our application, let’s create a new node that will subscribe to the /number topic. Each number that’s received will be added to a counter. We want to print the counter every time it’s updated.

As we did previously, let’s start the full explanations with Python, and then see the syntax specificities with C++.

Writing a Python subscriber

You can find the complete code for this Python node on GitHub. Many things we need to do here are identical to what we did previously, so I won’t fully detail every step. Instead, we will focus on the most important things so that we can write the subscriber.

Creating a Python node with a subscriber

Create a new node named number_counter inside the my_py_pkg package:

$ cd ~/ros2_ws/src/my_py_pkg/my_py_pkg/
$ touch number_counter.py
$ chmod +x number_counter.py

In this file, you can write the code for the node and add a subscriber. Here’s the...