Real Python: Build a Tic-Tac-Toe Game Engine With an AI Player in Python

When you’re a child, you learn to play tic-tac-toe, which some people know as naughts and crosses. The game remains fun and challenging until you enter your teenage years. Then, you learn to program and discover the joy of coding a virtual version of this two-player game. As an adult, you may still appreciate the simplicity of the game by using Python to create an opponent with artificial intelligence (AI).

By completing this detailed step-by-step adventure, you’ll build an extensible game engine with an unbeatable computer player that uses the minimax algorithm to play tic-tac-toe. Along the way, you’ll dive into immutable class design, generic plug-in architecture, and modern Python code practices and patterns.

In this tutorial, you’ll learn how to:

• Create a reusable Python library with the tic-tac-toe game engine
• Model the domain of tic-tac-toe following Pythonic code style
• Implement artificial players including one based on the minimax algorithm
• Build a text-based console front end for the game with a human player
• Explore strategies for performance optimizations

Click the link below to download the complete source code for this project:

Demo: Tic-Tac-Toe AI Player in Python

By the end of this tutorial, you’ll have a highly reusable and extensible Python library with an abstract game engine for tic-tac-toe. It’ll encapsulate universal game rules and computer players, including one that never loses due to bare-bones artificial intelligence support. In addition, you’ll create a sample console front end that builds on top of your library and implements a text-based interactive tic-tac-toe game running in the terminal.

Here’s what actual gameplay between two players might look like:

Generally, you may mix and choose the players from among a human player, a dummy computer player making moves at random, and a smart computer player sticking to the optimal strategy. You can also specify which player should make the first move, increasing their chances of winning or tying.

Later, you’ll be able to adapt your generic tic-tac-toe library for different platforms, such as a windowed desktop environment or a web browser. While you’ll only follow instructions on building a console application in this tutorial, you can find Tkinter and PyScript front end examples in the supporting materials.

The Tkinter front end is a streamlined version of the same game that’s described in a separate tutorial, which only serves as a demonstration of the library in a desktop environment:

Unlike the original, it doesn’t look as slick, nor does it allow you to restart the game easily. However, it adds the option to play against the computer or another human player if you want to.

The PyScript front end lets you or your friends play the game in a web browser even when they don’t have Python installed on their computer, which is a notable benefit:

If you’re adventurous and know a little bit of PyScript or JavaScript, then you could extend this front end by adding the ability to play online with another human player through the network. To facilitate the communication, you’d need to implement a remote web server using the WebSocket protocol, for instance. Take a look at a working WebSocket client and server example in another tutorial to get an idea of how that might work.

It’s worth noting that each of the three front ends demonstrated in this section merely implement a different presentation layer for the same Python library, which provides the underlying game logic and players. There’s no unnecessary redundancy or code duplication across them, thanks to the clear separation of concerns and other programming principles that you’ll practice in this tutorial.

Project Overview

The project that you’re going to build consists of two high-level components depicted in the diagram below:

The first component is an abstract tic-tac-toe Python library, which remains agnostic about the possible ways of presenting the game to the user in a graphical form. Instead, it contains the core logic of the game and two artificial players. However, the library can’t stand on its own, so you’re also going to create a sample front end to collect user input from the keyboard and visualize the game in the console using plain text.

You’ll start by implementing the low-level details of the tic-tac-toe library, and then you’ll use those to implement a higher-level game front end in a bottom-up fashion. When you finish this tutorial, the complete file structure resulting will look like this: