It all begins in a Coordinator.py that didn't change since previous section. This file has a timer based function timer_callback that once (only once, at the very beginning) sends a message goToPose to a robot.
The robot is implemented in Robot.py. It receives the command (same as in previous section) and
calls one of Path Planners that it owns to get the path.
Then it calls the Path Follower's command() function with "start" command.
PathFollower (implemented in PathFollower.py) runs a simple finite automata: on start it calls "calculate", from "calculate" it calls "drive", which publishes driving commands for a robot. As the robot gets close enough to a current target point on a path, "drive" passes control to "calculate" again, and so on, until the driving is over.