Avoid updating nested lists in for loop

Question

I have a Python program that I want to create different lists in a for loop and then store these list in another list to create an array. I take one input list, modify it and append it to storage list, and then repeat. My problem is that when I update the next list in the loop all lists in the array also gets updated, so I end up with an array containing multiple identical lists.

array = []    
road = [1,0,0,0,0,0,0,0]
    array.append(road)

    for i in range(0,len(road)-1):
        if road[i] == 1:
            road[i] = 0
            road[i+1] = 1
        print(road)
        array.append(road)

The print(road) yields exactly what I want namely

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

but the array after the last iteration contains

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

and after the first iteration

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

What can I do to stop the array from updating when I'm changing the list in the for loop?

Answer 1

array.append(road)

Change this to

array.append(road[:])

to append a copy of the list. That way you have multiple different lists appended rather than the same list object appended repeatedly.

Answer 2

array.append(road)

Change this to

array.append(road[:])

to append a copy of the list. That way you have multiple different lists appended rather than the same list object appended repeatedly.