TicTacToe.py

# Tic Tac Toe

import random

try:
    input = raw_input
except NameError:
    pass

def drawBoard(board):
    # This function prints out the board that it was passed.

    # "board" is a list of 10 strings representing the board (ignore index 0)
    print(' ' + board[7] + ' | ' + board[8] + ' | ' + board[9])
    print('-----------')
    print(' ' + board[4] + ' | ' + board[5] + ' | ' + board[6])
    print('-----------')
    print(' ' + board[1] + ' | ' + board[2] + ' | ' + board[3])

def inputPlayerLetter():
    # Lets the player type which letter they want to be.
    # Returns a list with the player's letter as the first item, and the computer's letter as the second.
    letter = ''
    while letter not in ('X', 'O'):
        letter = input('Do you want to be X or O? ').upper()

    # the first element in the tuple is the player's letter, the second is the computer's letter.
    
    return ['X', 'O'] if letter == 'X' else ['O', 'X']

def whoGoesFirst():
    # Randomly choose the player who goes first.
    return random.choice(('computer', 'player'))

def playAgain():
    # This function returns True if the player wants to play again, otherwise it returns False.
    print('Do you want to play again? (yes or no)')
    return input().lower().startswith('y')

def makeMove(board, letter, move):
    if isSpaceFree(board,move):
        board[move] = letter
    else:
        raise Exception("makeMove: the field is not empty!")

def isWinner(bo, le):
    # Given a board and a player's letter, this function returns True if that player has won.
    # We use bo instead of board and le instead of letter so we don't have to type as much.
    return ((bo[7] == le and bo[8] == le and bo[9] == le) or # across the top
    (bo[4] == le and bo[5] == le and bo[6] == le) or # across the middle
    (bo[1] == le and bo[2] == le and bo[3] == le) or # across the bottom
    (bo[7] == le and bo[4] == le and bo[1] == le) or # down the left side
    (bo[8] == le and bo[5] == le and bo[2] == le) or # down the middle
    (bo[9] == le and bo[6] == le and bo[3] == le) or # down the right side
    (bo[7] == le and bo[5] == le and bo[3] == le) or # diagonal
    (bo[9] == le and bo[5] == le and bo[1] == le)) # diagonal

def getBoardCopy(board):
    # Make a duplicate of the board list and return it the duplicate.
    dupeBoard = []

    for i in board:
        dupeBoard.append(i)

    return dupeBoard

def isSpaceFree(board, move):
    # Return true if the passed move is free on the passed board.
    return board[move].isdigit()

def getPlayerMove(board):
    # Let the player type in his move.
    move = ' '
    while move not in '1 2 3 4 5 6 7 8 9'.split() or not isSpaceFree(board, int(move)):
        print('What is your next move? (1-9)')
        move = input()
    return int(move)

def chooseRandomMoveFromList(board, movesList):
    # Returns a valid move from the passed list on the passed board.
    # Returns None if there is no valid move.
    possibleMoves = [i for i in movesList if isSpaceFree(board, i)]
    return random.choice(possibleMoves) if possibleMoves else None

def getComputerMove(board, computerLetter):
    # Given a board and the computer's letter, determine where to move and return that move.
    playerLetter = 'O' if computerLetter == 'X' else 'X'

    # Here is our algorithm for our Tic Tac Toe AI:
    # First, check if we can win in the next move
    for i in range(1, 10):
        copy = getBoardCopy(board)
        if isSpaceFree(copy, i):
            makeMove(copy, computerLetter, i)
            if isWinner(copy, computerLetter):
                return i

    # Check if the player could win on his next move, and block them.
    for i in range(1, 10):
        copy = getBoardCopy(board)
        if isSpaceFree(copy, i):
            makeMove(copy, playerLetter, i)
            if isWinner(copy, playerLetter):
                return i

    # Try to take one of the corners, if they are free.
    move = chooseRandomMoveFromList(board, [1, 3, 7, 9])
    if move != None:
        return move

    # Try to take the center, if it is free.
    if isSpaceFree(board, 5):
        return 5

    # Move on one of the sides.
    return chooseRandomMoveFromList(board, [2, 4, 6, 8])

def isBoardFull(board):
    # Return True if every space on the board has been taken. Otherwise return False.
    for i in range(1, 10):
        if isSpaceFree(board, i):
            return False
    return True

def main():
    print('Welcome to Tic Tac Toe!')
    random.seed()
    while True:
        # Reset the board
        theBoard = [' '] * 10
        for i in range(9,0,-1):
            theBoard[i] = str(i)
        playerLetter, computerLetter = inputPlayerLetter()
        turn = whoGoesFirst()
        print('The ' + turn + ' will go first.')
        gameIsPlaying = True
    
        while gameIsPlaying:
            if turn == 'player':
                # Player's turn.
                drawBoard(theBoard)
                move = getPlayerMove(theBoard)
                makeMove(theBoard, playerLetter, move)
    
                if isWinner(theBoard, playerLetter):
                    drawBoard(theBoard)
                    print('Hooray! You have won the game!')
                    gameIsPlaying = False
                else:
                    if isBoardFull(theBoard):
                        drawBoard(theBoard)
                        print('The game is a tie!')
                        break
                    else:
                        turn = 'computer'
    
            else:
                # Computer's turn.
                move = getComputerMove(theBoard, computerLetter)
                makeMove(theBoard, computerLetter, move)
    
                if isWinner(theBoard, computerLetter):
                    drawBoard(theBoard)
                    print('The computer has beaten you! You lose.')
                    gameIsPlaying = False
                else:
                    if isBoardFull(theBoard):
                        drawBoard(theBoard)
                        print('The game is a tie!')
                        break
                    else:
                        turn = 'player'
    
        if not playAgain():
            break
        
if __name__ == "__main__":
    main()