How to assign value to 2d array in for loop

Question

I want to assign value to 2d array in for loop
This is my code

num = 0
n = 3
arr = [[0] * n] * n

for i in range(n):
    for j in range(n):
        arr[i][j] = num
        num +=1

The output I expected is

[0, 1, 2]
[3, 4, 5]
[6, 7, 8]

But actual output is

[6, 7, 8]
[6, 7, 8]
[6, 7, 8]

Is there any way to fix this?

Does this answer your question? List of lists changes reflected across sublists unexpectedly — Błotosmętek
– Błotosmętek, Commented Apr 30, 2020 at 18:37

Moosa Saadat · Accepted Answer · 2020-04-30 18:36:05Z

3

arr = [[0] * n] * n

It creates n copies of list. So, when you make a change in one list, all others are changed as well. You can change it to something like this:

arr = [[0 for j in n] for i in n]

answered Apr 30, 2020 at 18:36

Moosa Saadat

1,1871 gold badge9 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1