Pseudocode

     





  import random


  def drawBoard(board):

      print('   |   |')

      print(' ' + board[7] + ' | ' + board[8] + ' | ' + board[9])

      print('   |   |')

      print('-----------')

      print('   |   |')

      print(' ' + board[4] + ' | ' + board[5] + ' | ' + board[6])

      print('   |   |')

      print('-----------')

      print('   |   |')

      print(' ' + board[1] + ' | ' + board[2] + ' | ' + board[3])

      print('   |   |')

  def inputPlayerLetter():

      letter = ''

      while not (letter == 'X' or letter == 'O'):

          print('Do you want to be X or O?')

          letter = input().upper()

      if letter == 'X':

          return ['X', 'O']

      else:

          return ['O', 'X']

  def whoGoesFirst():

      if random.randint(0, 1) == 0:

          return 'computer'

      else:

          return 'player'

  def playAgain():

      print('Do you want to play again? (yes or no)')

      return input().lower().startswith('y')

  def makeMove(board, letter, move):

      board[move] = letter

  def isWinner(bo, le):

      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):

      dupeBoard = []




      for i in board:

          dupeBoard.append(i)




      return dupeBoard

  def isSpaceFree(board, move):

      return board[move] == ' '

  def getPlayerMove(board):

      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):

      possibleMoves = []

      for i in movesList:

       if isSpaceFree(board, i):

              possibleMoves.append(i)

      if len(possibleMoves) != 0:

          return random.choice(possibleMoves)

      else:

          return None

   def getComputerMove(board, computerLetter):

      if computerLetter == 'X':

          playerLetter = 'O'

     else:

         playerLetter = 'X'


     for i in range(1, 10):

         copy = getBoardCopy(board)

         if isSpaceFree(copy, i):

             makeMove(copy, computerLetter, i)

             if isWinner(copy, computerLetter):

                 return i

     for i in range(1, 10):

         copy = getBoardCopy(board)

         if isSpaceFree(copy, i):

             makeMove(copy, playerLetter, i)

             if isWinner(copy, playerLetter):

                return i

     move = chooseRandomMoveFromList(board, [1, 3, 7, 9])

     if move != None:

         return move

     if isSpaceFree(board, 5):

         return 5

     return chooseRandomMoveFromList(board, [2, 4, 6, 8])

 def isBoardFull(board):

     for i in range(1, 10):

         if isSpaceFree(board, i):

             return False

     return True

 print('Welcome to Tic Tac Toe!')

 while True:

     theBoard = [' '] * 10

     playerLetter, computerLetter = inputPlayerLetter()

     turn = whoGoesFirst()

     print('The ' + turn + ' will go first.')

     gameIsPlaying = True

     while gameIsPlaying:

         if turn == 'player':

             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:

             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