井字棋游戏（P88）

X="X"
O="O"
EMPTY=" "

def ask_yes_no(question):
    response=None
    while response not in("y","n"):
        response=input(question).lower()
    return response

def ask_number(question,low,high):
    response=None
    while response not in range(low,high):
        response=int(input(question))
    return response

def pieces():
    go_first=ask_yes_no("玩家是否先走(y/n):")
    if go_first=="y":
        print("\n玩家先走")
        human=X
        computer=O
    else:
        print("\n计算机先走")
        computer=X
        human=O
    return computer,human

def new_board():
    board=[]
    for square in range(9):
        board.append(EMPTY)
    return board

def display_board(board):
    board2=board[:]
    for i in range(len(board)):
        if board[i]==EMPTY:
            board2[i]=i
    print("\t",board2[0],"|",board2[1],"|",board2[2])
    print("\t","---------")
    print("\t",board2[3],"|",board2[4],"|",board2[5])
    print("\t","---------")
    print("\t",board2[6],"|",board2[7],"|",board2[8],"\n")
    
def legal_moves(board):
    moves=[]
    for square in range(9):
        if board[square]==EMPTY:
            moves.append(square)
    return moves

def winner(board):
    WAYS_TO_WIN=((0,1,2),(3,4,5),(6,7,8),(0,3,6),(1,4,7),(2,5,8),(0,4,8),(2,4,6))
    for row in WAYS_TO_WIN:
        if board[row[0]]==board[row[1]]==board[row[2]]!=EMPTY:
            winner=board[row[0]]
            return winner
    if EMPTY not in board:
        return "TIE"
    return False

def human_move(board,human):
    legal=legal_moves(board)
    move=None
    while move not in legal:
        move=ask_number("你走哪个位置？",0,9)
        if move not in legal:
            print("\n此位置已经落过子了")
    return move

def computer_move(board,computer,human):
    board=board[:]
    BEST_MOVES=(4,0,2,6,8,1,3,5,7)
    for move in legal_moves(board):
        board[move]=computer
        if winner(board)==computer:
            print("计算机下棋位置...",move)
            return move
        board[move]=EMPTY
    for move in legal_moves(board):
        board[move]=human
        if winner(board)==human:
            print("计算机下棋位置...",move)
            return move
        board[move]=EMPTY
    for move in BEST_MOVES:
        if move in legal_moves(board):
            print("计算机下棋位置...",move)
            return move
        
def next_turn(turn):
    if turn==X:
        return O
    else:
        return X
    
def main():
    computer,human=pieces()#赋值X或O
    turn=X
    board=new_board()#初始化棋盘
    display_board(board)#显示当前棋盘
    while not winner(board):
        if turn==human:
            move=human_move(board,human)
            board[move]=human
        else:
            move=computer_move(board,computer,human)
            board[move]=computer
        display_board(board)
        turn=next_turn(turn)
    the_winner=winner(board)
    if the_winner==computer:
        print("Computer Winner!\n")
    elif the_winner==human:
        print("You Win!\n")
    elif the_winner=="TIE":
        print("Tie!\n")

main()
input("按任意键退出游戏")