Modelling the Turtle Python library in CSP

Software verification is an important tool in establishing the reliability of critical systems. One
potential area of application is in the field of robotics, as robots take on more tasks in both day-to-
day areas and highly specialised domains. Robots are usually given a plan to follow, if there are
errors in this plan it will have negative consequences for the robot’s performance. The capability
to check plans for errors in advance could prevent this. Python is a popular programming language
in the robotics domain, through the use of the Robot Operating System (ROS) and various other
libraries. Python’s Turtle package provides a simple robotic-style agent, which we formally model
here using Communicating Sequential Processes (CSP). Our interactive toolchain CSP2Turtle with
CSP model and Python components, enables Turtle plans to be verified in CSP before being executed
in Python. This means that certain classes of errors can be avoided, and provides a starting point for
more detailed verification of Turtle programs and more complex robotic systems. We illustrate our
approach with examples of robot navigation and obstacle avoidance in a 2D grid-world.