Tic Tac Toe

import sys

Nothing=0
X=1
O=4

def whowins(board):
    b=board
    winningpos = (b[:3],b[3:6],b[6:9],b[:7:3],b[1:8:3],b[2:9:3],b[:9:4],b[2:7:2])
    winningpos = list(map(sum,winningpos))

    return O if (3*O) in winningpos else (X if (3*X) in winningpos else Nothing)



def whosnext(now):
    return O if now==X else X


def newboard(board,position,turn):
    board=board[:]
    board[position-1]=turn
    return board

def display(board):
    counter=1
    for x in board:
        if x==X:
            print(" X","|" if counter%3 else "\n",end="")
        elif x==O:
            print(" O","|" if counter%3 else "\n",end="")
        else:
            print("",counter,"|" if counter%3 else "\n",end="")
        counter+=1


def main():
    board=[Nothing]*9
    turn=O
    for i in range(9,0,-1):
        display(board)
        while True:
            try:
                field = int(input("Welches Feld wollen Sie besetzen? "))
            except ValueError:
                print("Zahl eingeben")
                continue
            if board[field-1]==Nothing:
                break
            else:
                print("Dieses Feld ist schon besetzt")
        turn = whosnext(turn)
        board = newboard(board,field,turn)

        if whowins(board)==O:
            print("Spieler 'O' gewinnt")
            input()
            sys.exit()
        elif whowins(board)==X:
            print("Spieler 'X' gewinnt")
            input()
            sys.exit()

    print("Unentschieden")
    input()
    sys.exit()

if __name__=="__main__":
    main()
    input()