Snake Game (Day 21)

The classic Snake game, built object-oriented with Python's turtle module. It is the day-21 assignment of Udemy's 100 Days of Code: The Complete Python Pro Bootcamp: a snake moves across a black 600 by 600 screen by itself and is steered with the arrow keys; it eats food, grows, and a score is shown at the top; the game is over when the head passes the wall or touches its own tail. Day 21 teaches class inheritance (Food and Scoreboard inherit from Turtle) and slicing (the tail is segments[1:]).

The game has no runtime dependencies. The code keeps the names of the lectures (Snake, create_snake, move, up, down, left, right, segments, head, game_is_on, Food, Scoreboard, refresh, extend, increase_score, game_over) so that you can compare it with your own solution.

This repository continues 020-snake-game and starts from its finished game; docs/project-plan.md tells how the work is split.

Status: the game is finished: the snake moves by itself, is steered with the arrow keys, eats food and grows, the score is shown, and the game is over at the wall or at the tail. It was adopted from the finished game of 020 and checked against the day-21 lectures; see docs/project-plan.md.

Requirements

• Python 3.13 or newer, with tkinter (the turtle module needs it).
• git, to clone the repository.
• Optional: Doxygen to build the source documentation.
• No runtime dependencies. The development tools (pytest, ruff, mypy) are installed into the virtual environment by the dev extra.

Set up

Clone the repository, then create a local virtual environment .venv in its root, upgrade pip and install the project with its development tools. The .venv folder is ignored by git.

git clone https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/021-snake-game.git
cd 021-snake-game

Windows powershell

python -m venv .venv
.\.venv\Scripts\Activate.ps1
python -m pip install --upgrade pip
python -m pip install -e ".[dev]"

If PowerShell refuses to run the activation script, allow scripts for this window only with Set-ExecutionPolicy -Scope Process -ExecutionPolicy RemoteSigned and activate again. Python from python.org includes tkinter.

Linux debian

Debian 13 or newer ships Python 3.13. On older releases install Python 3.13 separately.

sudo apt install python3 python3-venv python3-tk
python3 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
python -m pip install -e ".[dev]"

MacOS

brew install python@3.13 python-tk@3.13
python3.13 -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
python -m pip install -e ".[dev]"

Run

With the virtual environment active:

python -m snake_game

It opens a black 600 by 600 window titled "My Snake Game". The snake of three white squares starts in the middle and moves to the right by itself, 20 pixels every 0.1 seconds.

Key	Effect
Up, Down, Left, Right	Turn the snake

The snake never turns straight back onto itself: the arrow key opposite to the way it is going is ignored, even when two keys are pressed within one move.

A small blue circle, the food, appears at a random place. When the head comes closer to it than 15 pixels the snake eats it: the food moves to a new random place, the snake grows by one segment, and the score at the top of the window goes up by 1 (Score: 0, Score: 1, ...).

The game is over when the head passes the wall (more than 280 pixels from the centre on any side) or touches the tail (comes closer than 10 pixels to a segment behind it). The snake stops, the text GAME OVER appears in the middle of the window, the score stays where it is, and a click on the window closes it. You can also close the window with its close button at any time.

Run the tests

The tests need no display: they use fakes instead of real turtles.

pytest

The same checks that continuous integration runs:

python -m pytest
python -m ruff check src tests
python -m ruff format --check src tests
python -m mypy

Continuous integration

.gitea/workflows/ci.yml runs on Gitea Actions on every push and on every pull request. It sets up Python 3.13, upgrades pip, installs .[dev], then runs pytest, ruff (lint and format check) and mypy. It does not build the source documentation: run doxygen Doxyfile yourself, as the next section shows. No step opens a turtle window.

The workflow lives in .gitea/workflows and not in .github/workflows, so GitHub does not run it and pushing to the GitHub mirror needs no workflow permission.

Build the source documentation

The source is documented with Doxygen comments and the Doxyfile in the root. Install Doxygen (winget install DimitriVanHeesch.Doxygen on Windows, sudo apt install doxygen on Debian, brew install doxygen on macOS), then:

doxygen Doxyfile

The HTML is written to build/doxygen/index.html. A warning fails the build.

Project layout

.
├── .gitea/workflows/ci.yml    continuous integration (Gitea Actions)
├── docs/                      business case, plan, milestones, reviews
├── src/snake_game/            the game
│   ├── __init__.py
│   ├── __main__.py            starts the game: python -m snake_game
│   ├── constants.py           every constant of the game
│   ├── food.py                the Food class (inherits from Turtle)
│   ├── main.py                screen set-up and the main flow
│   ├── scoreboard.py          the Scoreboard class (inherits from Turtle)
│   └── snake.py               the Snake class
├── tests/                     pytest tests (fakes.py holds the fake turtle and screen)
├── Doxyfile                   source documentation settings
├── LICENSE
├── pyproject.toml             project configuration
└── README.md

Where the day-21 lessons are in the code, so that you can compare it with your own solution:

Day-21 lecture	Where it is
Class inheritance	Food(Turtle) in food.py and Scoreboard(Turtle) in scoreboard.py
Collisions with the food	Food.refresh, eat_food_if_close in main.py, FOOD_* in constants.py
The scoreboard	Scoreboard.update_scoreboard and Scoreboard.increase_score
The wall	Snake.hits_wall, WALL_LIMIT, and Scoreboard.game_over for the text
The tail and slicing	Snake.extend, Snake.add_segment and Snake.hits_tail, which loops over segments[1:]

License

GNU Affero General Public License v3.0 only. See LICENSE.