继承Python类的属性系统

Question

class Board:

    array = [[" ", " ", " "],
             [" ", " ", " "],
             [" ", " ", " "]]

    def reset(self):
        self.array = [[" ", " ", " "],
                      [" ", " ", " "],
                      [" ", " ", " "]]


class AI(Board):

    def __init__(self):
        self.array[0][0] = "X"


ai = AI()
board = Board() 
print(ai.array)  # [['X', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]
print(board.array)  # [['X', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]
ai.reset()
print(ai.array)  # [[' ', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]
print(board.array)  # [['X', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]

我的问题是，为什么ai.array改变了，而board.array改变了。如果它们是相互连接的，那么为什么当方法属于AI时，这两个属性没有一起更改。

Answer 1

这可以通过以下方式来理解：

• When you self.array to use or modify，如在expression self.array[0][0] = "X"中，然后单击

- first the instance is checked to see if it has such an attribute;
- if it does not, the type of the instance is checked for the attribute.

(这是对发生的事情的简化，但对于这种情况，您只需要知道这些)

表达式设置实例时，如您在

• self.array = [...]中所做的那样，您将直接在instance

上设置属性

所以在你的示例代码中：

print(ai.array)     # ai does not have an array, Board.array is returned
print(board.array)  # board does not have an array, Board.array is returned
ai.reset()          # this adds an attribute to ai
print(ai.array)     # ai **does** have an array, it is returned
print(board.array)  # board does not have an array, Board.array is returned