IndexError：检查矩阵内容时列表索引超出范围

Question

I am currently programming a version of a game called Othello, where you can choose how big the board should be (alternating from 4x4 to 10x10). Now when I am trying to insert a faulty message as when you input a coordinate that is outside the board area it does not work. At the moment the input as when you place the tile in a nonlegal move works as well as if you input just 1 coordinate or multiple coordinates (it should only be two as one for the x and y-coordinate)

(Sorry I know I have posted a very similar question but as I then solved this problem, when I continued with my work, the problem have popped up again)

     def isOnBoard(self, x, y):
         return x >= 0 and x <= self.size-1 and y >= 0 and y <= self.size-1 




     def legalMove(self, tile, startX, startY):
 if not self.isOnBoard(startX, startY) == False\
    or self.board[startX][startY] != ' '\
    or not self.isOnBoard(startX, startY):
     return False
     #(lots more down here that checks if the placed move is legal but nonrelevant to the question)


    def playerMove(self,tile): 

        while True:
            move = input().lower()
                if self.legalMove(tile, x, y) == False:
                    print('Wrong input, try again') #<--- checks that the input coordinate is legal
                else:
                    break
            else:
                print('this was wrong try again!.') #<-- checks that input coordinate just consists of two characters
        return [x, y]

if self.board[startX][startY] != ' ' or not self.isOnBoard(startX, startY): IndexError: list index out of range

Answer 1

I'd propose you change your legalMove function's definition. You don't need to pass isOnBoard as a parameter (and you don't, so why keep it?):

def legalMove(self, tile, startX, startY):

isOnBoard is defined, and checks whether indices are out of bounds or not. I would recommend making the call to isOnBoard inside legalMove . This way you complete the function, functionally. Here's the proposed changes:

def legalMove(self, tile, startX, startY):
     if not self.isOnBoard(startX, startY)\
        or self.board[startX][startY] != ' '\
        or not self.isOnBoard(startX, startY):
         return False

Answer 2

You need to check self.isOnBoard(startX, startY) before you check the value of self.board[startX][startY] . If the move is out of bounds (not on the board), then it will throw an exception if you try to access those indeces in the array, which is what you are experiencing.

Bad version:

if self.board[startX][startY] != ' ' or not self.isOnBoard(startX, startY):

Better version:

if not self.isOnBoard(startX, startY) or self.board[startX][startY] != ' ':

Because Python employs short-circuiting for conditionals, this is all you need.

The point is that the call to isOnBoard() must come strictly before any attempt to access the list. If you have an x,y coordinate pair that fails the isOnBoard() condition, that means one or both of the indexes are out of bounds by definition. Therefore, any attempt to access the list will most assuredly result in a list index out of range exception. So if you have a coordinate pair that fails isOnBoard(), then you must not attempt to check the list at those coordinates.