基于python纯函数实现井字棋游戏

\'\'\'全局变量：
 X 和 O 表示两方的棋子;
 EMPTY 表示棋位为空；
 TIE 表示平局；
 NUM_SQUARES 表示有 9 个棋位
 \'\'\'
 X = \"X\"
 O = \"O\"
 EMPTY = \" \"
 TIE = \"TIE\"
 NUM_SQUARES = 9

def ask_yes_no(question):
  \'\'\'问一个是或否的问题，用 y 或 n 回答。\'\'\'
  response = None
  while response not in (\'y\', \'n\'):
    response = input(question).lower()
  return response


def ask_number(question, low, high):
  \'\'\'讯问一个规定范围的数字。\'\'\'
  response = None
  while response not in range(low, high):
    response = int(input(question))
  return response


def pieces():
  \'\'\'决定在人和机器之间谁先行棋。\'\'\'
  go_first = ask_yes_no(\'你先走？ (y/n): \')
  if go_first == \'y\':
    print(\'\\n好，你先请。\')
    human = X
    computer = O
  else:
    print(\'\\n你放弃先手，我先走。\')
    computer = X
    human = O
  return computer, human


def new_board():
  \'\'\'创建一个棋盘。\'\'\'
  board = []
  for square in range(NUM_SQUARES):
    board.append(EMPTY)
  return board


def display_board(board):
  \'\'\'显示棋盘。\'\'\'
  print(\'\\n\\t\', board[0], \'|\', board[1], \'|\', board[2])
  print(\'\\t\', \'---------\')
  print(\'\\t\', board[3], \'|\', board[4], \'|\', board[5])
  print(\'\\t\', \'---------\')
  print(\'\\t\', board[6], \'|\', board[7], \'|\', board[8], \'\\n\')


def legal_moves(board):
  \'\'\'创建合法的行棋位置清单。\'\'\'
  moves = []
  for square in range(NUM_SQUARES):
    if board[square] == EMPTY: # 该棋位为空
      moves.append(square)
  return moves


def winner(board):
  \'\'\'判定游戏获胜者。\'\'\'
  WAYS_TO_WIN = ((0, 1, 2), # 横
          (3, 4, 5),
          (6, 7, 8),
          (0, 3, 6), # 竖
          (1, 4, 7),
          (2, 5, 8),
          (0, 4, 8), # 主对角线
          (2, 4, 6)) # 副对角线
  # 谁先有三个棋子在一条直线上谁就获胜。
  for row in WAYS_TO_WIN:
    if board[row[0]] == board[row[1]] == board[row[2]] != EMPTY:
      winner = board[row[0]]
      return winner
  
  # 没有获胜方，但棋盘已经下满，判为平局
  if EMPTY not in board:
    return TIE

  return None # 没有获胜方，且非平局


def human_move(board, human):
  \'\'\'获取玩家的行棋位置。\'\'\' 
  legal = legal_moves(board) # 合法的行棋位置清单
  move = None
  while move not in legal:
    move = ask_number(\'你走哪？ (0 - 8):\', 0, NUM_SQUARES)
    if move not in legal:
      print(\'\\n你选的棋位已落子，重新选择。\\n\')
  print(\'落子无悔...\')
  return move


def computer_move(board, computer, human):
  \'\'\'获取电脑的行棋位置。\'\'\'
  
  board = board[:] # 通过切片复制棋盘, 创建局部变量
  BEST_MOVES = (4, 0, 2, 6, 8, 1, 3, 5, 7) # 优先的行棋位置

  print(\'我走到：\', end=\' \')
  
  # 在局部空间确定可以获胜的走法
  for move in legal_moves(board): # 合法的行棋位置列表
    board[move] = computer # 更新棋盘副本
    if winner(board) == computer:
      # 计算机能获胜
      print(move)
      return move
    # 如果计算机在该棋位行棋不能获胜，
    board[move] = EMPTY # 悔棋，更换下一个合法棋位
  
  # 阻止玩家获胜
  for move in legal_moves(board): # 合法的行棋位置列表
    board[move] = human # 更新棋盘
    if winner(board) == human:
      # 在该棋位玩家行棋后将获胜
      print(move)
      return move
    # 玩家不能获胜，不行棋至此
    board[move] = EMPTY

  # 没有能使行棋双方立决胜负的棋位，从优先棋位选择合法行棋位置
  for move in BEST_MOVES:
    if move in legal_moves(board):
      print(move)
      return move


def next_turn(turn):
  \'\'\'切换行棋方\'\'\'
  if turn == X:
    return O
  else:
    return X

  
def congrat_winner(the_winner, computer, human):
  \'\'\'向获胜方表示祝贺或声明平局\'\'\'
  if the_winner != TIE:
    print(the_winner, \'祝贺你！\\n\')
  else:
    print(\'平局。。。\\n\')

  if the_winner == computer:
    print(\'如我所料，我又胜了。\\n这是否能说明计算机在给方面都优于人类呢？\')

  elif the_winner == human:
    print(\'真是匪夷所思，你没捣鬼吧？人类怎么会胜？ \\n不会有下次了。\' )

  elif the_winner == TIE:
    print(\'你很厉害嘛，能跟计算机打成平手。\')

def main():
  display_instruct() # 显示游戏操作指南
  computer, human = pieces() # 决定谁先行棋
  turn = X # 先行棋方执子 X
  board = new_board() # 创建空棋盘
  display_board(board) # 显示棋盘

  while not winner(board): 
    # 判定结果，在没有获胜方且不是平局时进入循环
    if turn == human:
      # 轮到玩家行棋，玩家行棋
      move = human_move(board, human) # 玩家的行棋位置
      board[move] = human # 更新棋盘
    else:
      # 轮到电脑行棋
      move = computer_move(board, computer, human) # 电脑的行棋位置
      board[move] = computer # 更新棋盘
    display_board(board) # 显示更新后的棋盘
    turn = next_turn(turn) # 切换行棋方

  the_winner = winner(board) # 判定获胜者，返回获胜方的执子，平局返回 None
  congrat_winner(the_winner, computer, human) # 向获胜方表示祝贺或声明是平局

main()
input(\'\\n\\n按回车键退出程序。\') # 等待用户