python对象属性改变值

Question

我正在嵌套循环中创建单元格对象的网格（二维列表）。在实例化每个单元后，我立即打印了它们的属性值。退出循环后，我再次循环单元格并重新打印它们的属性值。某些值似乎未更改（self.xlo），而某些属性似乎已被最后一个单元格的属性值（self.ylo、self.path）替换。 2 个打印语句是相同的，并且遵循相同的嵌套循环。为什么结果不同？

mps = ['xxxxxx',
       'xoooox',
       'xoxxox',
       'xoooox',
       'xxxxxx']
ROWS = len(mps)     # equals 5
COLS = len(mps[0])  # equals 6
SCRW = 600
SCRH = 300
CELW = int(SCRW/COLS)
CELH = int(SCRH/ROWS)


class cell():
    def __init__(self, row, col, path):
        self.row = row
        self.col = col
        self.path = path
        self.xlo = int(col*CELW)
        self.ylo = int(row*CELH)
        return

row_blank = ['']*COLS
grid = [row_blank]*ROWS
path_list = []
for r in range(ROWS):
    for c in range(COLS):
        is_path = (mps[r][c]=='o')
        grid[r][c] = cell(r,c, is_path)
        print(f'cell {r},{c} position {grid[r][c].xlo},{grid[r][c].ylo} and path {grid[r][c].path}')
        
print("\n==============Re-Printing to check!")
for r in range(ROWS):
    for c in range(COLS):
        print(f'cell {r},{c} position {grid[r][c].xlo},{grid[r][c].ylo} and path {grid[r][c].path}')
    
exit()

感谢您的指导 - 我似乎在使用 python OOP 对象时犯了一个非常根本的错误。打印语句的结果如下 - 第一组是正确的，重新打印有变化。

cell 0,0 position 0,0 and path False
cell 0,1 position 100,0 and path False
cell 0,2 position 200,0 and path False
cell 0,3 position 300,0 and path False
cell 0,4 position 400,0 and path False
cell 0,5 position 500,0 and path False
cell 1,0 position 0,60 and path False
cell 1,1 position 100,60 and path True
cell 1,2 position 200,60 and path True
cell 1,3 position 300,60 and path True
cell 1,4 position 400,60 and path True
cell 1,5 position 500,60 and path False
cell 2,0 position 0,120 and path False
cell 2,1 position 100,120 and path True
cell 2,2 position 200,120 and path False
cell 2,3 position 300,120 and path False
cell 2,4 position 400,120 and path True
cell 2,5 position 500,120 and path False
cell 3,0 position 0,180 and path False
cell 3,1 position 100,180 and path True
cell 3,2 position 200,180 and path True
cell 3,3 position 300,180 and path True
cell 3,4 position 400,180 and path True
cell 3,5 position 500,180 and path False
cell 4,0 position 0,240 and path False
cell 4,1 position 100,240 and path False
cell 4,2 position 200,240 and path False
cell 4,3 position 300,240 and path False
cell 4,4 position 400,240 and path False
cell 4,5 position 500,240 and path False

==============Re-Printing to check!
cell 0,0 position 0,240 and path False
cell 0,1 position 100,240 and path False
cell 0,2 position 200,240 and path False
cell 0,3 position 300,240 and path False
cell 0,4 position 400,240 and path False
cell 0,5 position 500,240 and path False
cell 1,0 position 0,240 and path False
cell 1,1 position 100,240 and path False
cell 1,2 position 200,240 and path False
cell 1,3 position 300,240 and path False
cell 1,4 position 400,240 and path False
cell 1,5 position 500,240 and path False
cell 2,0 position 0,240 and path False

Process ended with exit code 0.

>

Answer 1

问题出在这两行：

row_blank = ['']*COLS
grid = [row_blank]*ROWS

以这种方式创建列表时，最终会得到包含多个对 same 行对象的引用的“网格”。

您可以使用以下代码进行检查：

for row in grid:
    print(id(row))

输出（确切的数字无关紧要，重要的是它是相同的数字 - 这意味着相同的对象：

1714813861696
1714813861696
1714813861696
1714813861696
1714813861696

相反，您应该像这样初始化网格，这确保每一行都是唯一的对象。

grid = [['' for _ in range(COLS)] for _ in range(ROWS)]