Python：中断函数的执行

Question

I'm new to Python and trying to build a tic-tac-toe game. I guess there are a ton of solutions on the internet, but I wanted to try it without looking at them. Now halfway through I ran into a problem: The function def player_input(board) works as intended when I input a position that's not already taken. However, when there is already a marker "X" or "O" there, I want if board[marker_pos] == "X" or board[marker_pos] == "O": to catch this and start the function again, so the user sees the input field again.

It does that, but as you can see below in the two pictures, when I try to put the mark in an already occupied field, the function seems to execute completely. I thought it would get interrupted when I call the function from within itself (player_input(board) ). So it shows me the result of display_board(board) and print "iTurn is %s " %iTurn twice or however many tries it took me to put the mark in an empty position.

from IPython.display import clear_output

    def intro():
        board = [0]*9
        print "Player1, your marker is 'X'."
        print "Player2, your marker is 'O'."
        global iTurn
        iTurn = 1 

    def display_board(board):
        print "    |   |"
        print "  " + str(board[6]) + " | "  + str(board[7]) + " | "  + str(board[8]) 
        print "-------------"
        print "  " + str(board[3]) + " | "  + str(board[4]) + " | "  + str(board[5]) 
        print "-------------"
        print "  " + str(board[0]) + " | "  + str(board[1]) + " | "  + str(board[2]) 
        print "    |   |"


    def player_input(board):
        global iTurn
        if iTurn%2 != 0:
            marker_pos = input("Player1, please write which position (1 through 9) your marker should go")
        else:
            marker_pos = input("Player2, please write which position (1 through 9) your marker should go")     
        marker_pos -= 1

        if marker_pos < 0 or marker_pos > 8:
            print "Position needs to be between 1 and 9."
            player_input(board)

        else:
            if  board[marker_pos] == "X" or board[marker_pos] == "O":
                print "Position is already occupied."
                player_input(board)
            elif iTurn%2 != 0:
                board[marker_pos] = "X"
            else:
                board[marker_pos] = "O"    
        iTurn += 1
        print "iTurn is %s " %iTurn
        #check_winning(board)
        display_board(board)

edit: This would be the code for the while loop

while (marker_pos < 0 or marker_pos > 8) or (board[marker_pos] == "X" or board[marker_pos] == "O"):
    if (marker_pos < 0 or marker_pos > 8):
        print "Position needs to be between 1 and 9."
    elif (board[marker_pos] == "X" or board[marker_pos] == "O"):
        print "Position is already occupied."
    marker_pos = input("Please write where your marker should go (1 through 9).")
    marker_pos -= 1

Answer 1

I think the problem is, that you don't exit the function which got an invalid position. That's why - after the player_input with the valid position is run - the one called before also runs the last commands. This can be fixed if you simply return after calling player_input again.

Change the player_input(board) s to

return player_input(board)

or

player_input(board)
return

Answer 2

You can use while True to repeat it and break to exit loop

def player_input(board):
    global iTurn

    while True:
        if iTurn%2 != 0:
            marker_pos = input("Player1, please write which position (1 through 9) your marker should go")
        else:
            marker_pos = input("Player2, please write which position (1 through 9) your marker should go")     
        marker_pos -= 1

        if marker_pos < 0 or marker_pos > 8:
            print "Position needs to be between 1 and 9."
        else:
            if  board[marker_pos] == "X" or board[marker_pos] == "O":
                print "Position is already occupied."
            elif iTurn%2 != 0:
                board[marker_pos] = "X"
                break
            else:
                board[marker_pos] = "O"
                break

    iTurn += 1
    print "iTurn is %s " %iTurn
    display_board(board)

---

You can write it little simpler

def player_input(board):
    global iTurn

    if iTurn%2 != 0:
        text = "Player1, please write which position (1 through 9) your marker should go"
        mark = "X"
    else:
        text = "Player2, please write which position (1 through 9) your marker should go"        
        mark = "O"

    while True:
        marker_pos = input(text)
        marker_pos -= 1

        if marker_pos < 0 or marker_pos > 8:
            print "Position needs to be between 1 and 9."
        else:
            if board[marker_pos] != 0:
                print "Position is already occupied."
            else:
                board[marker_pos] = mark
                break

    iTurn += 1
    print "iTurn is %s " % iTurn
    display_board(board)