I have got a simple naughts and crosses game working, can someone tell me a simple def blah(): .. command to check if the player has already moved to a place on the board already taken.. E.G Player's first go = top left Player's second go = top left.. (message comes up saying please have another go)?

How would i do that? The code i have is this.

Row1 = [" "," "," "]
Row2 = [" "," "," "]
Row3 = [" "," "," "]
Grid = [Row1,Row2,Row3]


Won = False


def check():
    if Grid[0][0] == 'X' and  Grid[0][1] == 'X' and Grid[0][2] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[1][0] == 'X' and  Grid[1][1] == 'X' and Grid[1][2] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[2][0] == 'X' and  Grid[2][1] == 'X' and Grid[2][2] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[0][0] == 'X' and  Grid[1][0] == 'X' and Grid[2][0] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[0][1] == 'X' and  Grid[1][1] == 'X' and Grid[2][1] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[0][2] == 'X' and  Grid[1][2] == 'X' and Grid[2][2] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[0][0] == 'X' and  Grid[1][1] == 'X' and Grid[2][2] == 'X':
        print("player 1 wins!")
        return True
    elif Grid[2][0] == 'X' and  Grid[1][1] == 'X' and Grid[0][2] == 'X':
        print("player 1 wins!")
        return True

    if Grid[0][0] == 'O' and  Grid[0][1] == 'O' and Grid[0][2] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[1][0] == 'O' and  Grid[1][1] == 'O' and Grid[1][2] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[2][0] == 'O' and  Grid[2][1] == 'O' and Grid[2][2] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[0][0] == 'O' and  Grid[1][0] == 'O' and Grid[2][0] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[0][1] == 'O' and  Grid[1][1] == 'O' and Grid[2][1] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[0][2] == 'O' and  Grid[1][2] == 'O' and Grid[2][2] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[0][0] == 'O' and  Grid[1][1] == 'O' and Grid[2][2] == 'O':
        print("player 2 wins!")
        return True
    elif Grid[2][0] == 'O' and  Grid[1][1] == 'O' and Grid[0][2] == 'O':
        print("player 2 wins!")
        return True



def NAC():
    DisplayGrid()
    while Won == False:

        YourGo = input ("Your go\nEnter Number -  ")

        if YourGo == '7':
            Grid[0][0] = 'X'


        elif YourGo == '8':
            Grid[0][1] = 'X'

                                    #Player one's turn
        elif YourGo == '9':
            Grid[0][2] = 'X'


        elif YourGo == '4':
            Grid[1][0] = 'X'


        elif YourGo == '5':
            Grid[1][1] = 'X'


        elif YourGo == '6':
            Grid[1][2] = 'X'


        elif YourGo == '1':
            Grid[2][0] = 'X'


        elif YourGo == '2':
            Grid[2][1] = 'X'


        elif YourGo == '3':
            Grid[2][2] = 'X'

        DisplayGrid()

        if check() == True: break



        YourGo2 = input("Play 2's turn\nEnter number - ")       
        if YourGo2 == '7':
            Grid[0][0] = 'O'


        elif YourGo2 == '8':            #player Two's turn
            Grid[0][1] = 'O'


        elif YourGo2 == '9':
            Grid[0][2] = 'O'


        elif YourGo2 == '4':
            Grid[1][0] = 'O'


        elif YourGo2 == '5':
            Grid[1][1] = 'O'

        elif YourGo2 == '6':
            Grid[1][2] = 'O'


        elif YourGo2 == '1':
            Grid[2][0] = 'O'


        elif YourGo2 == '2':
            Grid[2][1] = 'O'


        elif YourGo2 == '3':
            Grid[2][2] = 'O'


        if check() == True: break

        DisplayGrid()
        check()


def DisplayGrid():
    print("  -----------")
    DisplayRow(Grid[0][0],Grid[0][1],Grid[0][2])
    print("  -----------")
    DisplayRow(Grid[1][0],Grid[1][1],Grid[1][2])
    print("  -----------")
    DisplayRow(Grid[2][0],Grid[2][1],Grid[2][2])
    print("  -----------")

def DisplayRow (a,b,c):
    print(" | ",end="")
    print(a,end="")
    print(" | ",end="")
    print(b,end="")
    print(" | ",end="")
    print(c,end="")
    print(" |")


NAC()
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