Mars rover kata in Python

Overview

This kata complements Clean Code: Advanced TDD, Ep. 20.

This repository contains several exercises designed to improve your skills in test-driven development.

Instructions

As a NASA engineer, you are part of the team that explores Mars by sending remotely controlled vehicles to the planet's surface. You need to develop a control software that translates the commands sent from Earth to instructions that the rover understands.

NASA engineers treat the surface of Mars as a square grid, with side length being a power of two, e.g., 4x4, 8x8, 16x16, etc.

On the grid, the rover's location is defined by coordinates (x, y) and an orientation represented by one of the four compass directions (N, S, W, or E). Coordinates (0, 0) represent the bottom left corner of the grid.

Given an initial rover's location, NASA sends commands encoded as a sequence (string) of characters with the following meaning:

• 'L' and 'R' turn the rover 90 degrees left or right, respectively;
• 'F' and 'B' move the rover forward or backward one grid point.

Exercise 1

For Opportunity, the grid had the torus (or "donut") topology, where (think games like Snake or Pacman) the rover vanishes on the top and reappears on the bottom (and visa versa for left and right).

Note

In a 4x4 grid, the following table shows the resulting position for a movement on the grid (edge cases shown in bold):

Position	x + 1	x - 1	y + 1	y - 1
(0, 0)	(1, 0)	(3, 0)	(0, 1)	(0, 3)
(1, 0)	(2, 0)	(0, 0)	(1, 1)	(1, 3)
(1, 1)	(2, 1)	(0, 1)	(1, 2)	(1, 0)

Your task is to implement Opportunity's control software.

Exercise 2

For Curiosity, NASA decided to improve the accuracy of their grid system by using a Polar coordinate system. This interpretation of the grid system lends itself to the concept of latitude and longitude: the sphere is sliced into an even number of latitudes (central lines) and longitudes (evenly spaced lines from North to South pole). In this model, coordinates (x, y) become abstract representations of longitudes and latitudes.

While this model is closer to planets, it produces some significant edge cases that complicate the control system. For example, the behavior is undefined at the poles if we want the poles to be represented through the coordinates.

The chief engineer decided to constrain the solution to the following: the poles are not "on the grid," so the rover moves "over" them but never rests on them.

Note

In a 4x4 grid, the following table shows the resulting position for a movement on the grid (edge cases shown in bold):

Position	x + 1	x - 1	y + 1	y - 1
(0, 0)	(1, 0)	(3, 0)	(0, 1)	(2, 0)
(1, 0)	(2, 0)	(0, 0)	(1, 1)	(3, 0)
(1, 1)	(2, 1)	(0, 1)	(1, 2)	(1, 0)

Your task is to extend the rover control software that you created for Opportunity to support this new "polar" grid topology. The control software should still support the older "torus" topology, and your implementation should provide a way to select the desired topology.

Exercise 3

Now, each grid point might contain an obstacle, so we need to implement obstacle detection. If a given sequence of commands encounters an obstacle, the rover moves up to the last possible point, aborts the sequence, and reports the obstacle by throwing an exception.

Your task is to extend the rover control software to support obstacle detection.

Setup is complete when the existing test suite passes.

Prerequisites

Required:

• Git
• uv

Optional:

• GNU Make, for shorter commands. Every required task also has a direct uv command.

You do not need to install Python or pytest separately. uv installs a compatible Python version and the locked project dependencies when needed.

Set up the kata

1. Clone the repository:

   git clone https://github.com/Coding-Cuddles/mars-rover-python-kata.git

2. Enter the repository directory:

   cd mars-rover-python-kata

3. Run the existing tests. Use Make when it is installed:

   make test

   Otherwise, run pytest through uv directly:

   uv run pytest

   The first run may install Python and the project dependencies. Setup is complete when pytest reports 1 passed.

   If the command fails with uv: command not found, install uv and repeat this step.

Work on the kata

Implement the exercises in mars_rover.py. The initial behavior is covered by test_mars_rover.py.

Run the tests after each change. Use Make when it is installed:

make test

Otherwise, run pytest through uv directly:

uv run pytest

Continue when the test run passes.

Make command reference

Make is optional. Run make or make help to list these commands in the terminal.

Command	Result
make all	Run the test suite
make help	Show the command reference
make test	Run the test suite
make format	Format tracked Python files
make format-check	Check formatting without changing files
make clean	Remove generated caches

Credits and references

• https://kata-log.rocks/mars-rover-kata