Build a Tic-Tac-Toe Game in Python: Complete Code

Quick answer: Learn how to build a two-player Tic-Tac-Toe game in Python using lists, functions and loops, with complete working code and a win-checking algorithm.

What You Will Build

A console based two-player Tic-Tac-Toe game using a 3x3 board represented as a list, alternating turns, and checking for a win or a draw after each move.

Representing the Board

board = [' ' for _ in range(9)]   # 9 empty cells, indexed 0 to 8

def print_board():
    for row in range(0, 9, 3):
        print(f" {board[row]} | {board[row+1]} | {board[row+2]} ")
        if row < 6:
            print("---+---+---")

Checking for a Winner

def check_winner(player):
    winning_combos = [
        [0, 1, 2], [3, 4, 5], [6, 7, 8],   # rows
        [0, 3, 6], [1, 4, 7], [2, 5, 8],   # columns
        [0, 4, 8], [2, 4, 6]               # diagonals
    ]
    for combo in winning_combos:
        if all(board[i] == player for i in combo):
            return True
    return False

The Main Game Loop

def play_game():
    current_player = 'X'

    for turn in range(9):
        print_board()
        move = int(input(f"Player {current_player}, choose a cell (0-8): "))

        if board[move] != ' ':
            print("Cell already taken, try again")
            continue

        board[move] = current_player

        if check_winner(current_player):
            print_board()
            print(f"Player {current_player} wins!")
            return

        current_player = 'O' if current_player == 'X' else 'X'

    print_board()
    print("It's a draw!")

play_game()

How the Win Check Works

The board's 9 cells are indexed 0 to 8. The 8 possible winning lines, 3 rows, 3 columns and 2 diagonals, are stored as index combinations. all(board[i] == player for i in combo) checks whether every cell in a given combination belongs to the same player.

Possible Improvements

• Add input validation to reject a move index outside 0 to 8

• Build a simple AI opponent using the minimax algorithm

• Add a graphical interface using Tkinter instead of the console

Common Interview Questions

How would you represent a Tic-Tac-Toe board in code?

A common approach is a flat list of 9 elements, indexed 0 to 8, rather than a nested 3x3 list, since it simplifies checking the 8 winning combinations as fixed index lists.

How would you check for a draw?

If all 9 cells are filled and check_winner() has not returned true for either player, the game is a draw, which this implementation handles by simply completing all 9 turns without an early win.