Python 中矩阵中单元格的值分配

Question

我在下面有我的代码。 我想要做的是更新 Python 矩阵中的单个值（i，j）。 当我执行分配时，值将更新为整个列而不是单个单元格。 我想知道为什么会这样。

这是代码：

grid =   [
            [1,0,0,0],
            [1,0,0,0], 
            [0,0,0,0],
            [0,1,0,0]
        ]
def distance(p1,p2): 
            x1,y1 = p1
            x2,y2 = p2 
            
            return abs(x1-x2) + abs(y1-y2)
        
land= [] 
row = len(grid)
columns = len(grid[0])
for i in range(row): 
    for j in range(columns): 
        if grid[i][j]==1: 
            land.append((i,j))



max_distance = -1

new_grid_row = [0]*len(grid[0])
new_grid = [new_grid_row]* len(grid)

def print_grid(new_grid): 
    print('=======') 
    print('')
    print('')
    for x in new_grid: 
        print(x)
    print('')
    print('')
    print('=======')
    

print_grid(new_grid)

for i in range(row): 
    for j in range(columns): 
        p2 = (i,j) 
        val = min([distance(p1,p2) for p1 in land])
        print(i,j,p2,val)
        new_grid[i][j] = val # I just want to update a single cell, but the whole column is being updated. Why?
        print_grid(new_grid)

这是程序的output：

=======


[0, 0, 0, 0]
[0, 0, 0, 0]
[0, 0, 0, 0]
[0, 0, 0, 0]


=======
(0, 0, (0, 0), 0)
=======


[0, 0, 0, 0]
[0, 0, 0, 0]
[0, 0, 0, 0]
[0, 0, 0, 0]


=======
(0, 1, (0, 1), 1)
=======


[0, 1, 0, 0]
[0, 1, 0, 0]
[0, 1, 0, 0]
[0, 1, 0, 0]


=======
(0, 2, (0, 2), 2)
=======


[0, 1, 2, 0]
[0, 1, 2, 0]
[0, 1, 2, 0]
[0, 1, 2, 0]


=======
(0, 3, (0, 3), 3)
=======


[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]


=======
(1, 0, (1, 0), 0)
=======


[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]


=======
(1, 1, (1, 1), 1)
=======


[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]


=======
(1, 2, (1, 2), 2)
=======


[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]


=======
(1, 3, (1, 3), 3)
=======


[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2, 3]


=======
(2, 0, (2, 0), 1)
=======


[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]


=======
(2, 1, (2, 1), 1)
=======


[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]


=======
(2, 2, (2, 2), 2)
=======


[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]


=======
(2, 3, (2, 3), 3)
=======


[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]


=======
(3, 0, (3, 0), 1)
=======


[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]
[1, 1, 2, 3]


=======
(3, 1, (3, 1), 0)
=======


[1, 0, 2, 3]
[1, 0, 2, 3]
[1, 0, 2, 3]
[1, 0, 2, 3]


=======
(3, 2, (3, 2), 1)
=======


[1, 0, 1, 3]
[1, 0, 1, 3]
[1, 0, 1, 3]
[1, 0, 1, 3]


=======
(3, 3, (3, 3), 2)
=======


[1, 0, 1, 2]
[1, 0, 1, 2]
[1, 0, 1, 2]
[1, 0, 1, 2]


=======