Is this a module, script, package?

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Sounds a valid, common confusion regarding ROS/Catkin software written in Python. Both Python and ROS/Catkin define "package", in the way I'd say essentially the same, at least from folder structure perspective.

• See Python packages (docs.python.org) for Python package concept.
• See Catkin conceptual overview for Catkin package concept.

The repo in question consits of 2 folders at the time of writing. - motor_control_bus folder seems to be NOT a ROS/Catkin package. It's missing minimal files that are required to be a Catkin package. - diff_car_controller seems to be a Catkin package (I haven't tried building/running it).

What you can do to use motor_control_bus folder via ROS is to make it "catkinized" by adding the missing required files (so that the folder can be "built" by Catkin, then Python modules in the folder will be accessible via ROS tools, e.g. rospack, rosrun, roslaunch).