Can you explain me why outpot is so?

if __name__ == '__main__':
    N = int(input())
    lst = []
    nums = []
        
    for i in range(N):
        a = input()
        temp = a.split()
        if 'insert' in temp:
            lst.insert(int(temp[1]), int(temp[2]))
        elif 'print' in temp:
            nums.append(lst)
        elif 'remove' in temp:
            del lst[lst.index(int(temp[1]))]
        elif 'append' in temp:
            lst.append(int(temp[1]))
        elif 'sort' in temp:
            lst.sort()
        elif 'pop' in temp:
            lst.pop(-1)
        elif 'reverse' in temp:
            lst = lst.reverse()
    for i in nums:
        print(i)

Input

    12

    insert 0 5

    insert 1 10

    insert 0 6

    print

    remove 6

    append 9

    append 1

    sort

    print

    pop

    reverse

    print

Output

    [9, 5, 1]

    [9, 5, 1]

    None

Expected output

    [6, 5, 10]

    [1, 5, 9, 10]

    [9, 5, 1]

I am doing task on HackerRank and I almost have done it, but suddenly in every loop in ‘for i in range(N)’ program add the last list three times independent on Input.

I have tried a lot of debug tests, but I can’t find mistake in my script.

>Solution :

Two things that need to change:

1. lst.reverse() instead of lst = lst.reverse()
2. As you are appending, removing etc. to lst, the list that you saved in nums will change with it. You need to use nums.append(lst.copy()) instead of nums.append(lst)

The full code becomes:

if __name__ == '__main__':
    N = int(input())
    lst = []
    nums = []

    for i in range(N):
        a = input()
        temp = a.split()
        if 'insert' in temp:
            lst.insert(int(temp[1]), int(temp[2]))
        elif 'print' in temp:
            nums.append(lst.copy())
        elif 'remove' in temp:
            del lst[lst.index(int(temp[1]))]
        elif 'append' in temp:
            lst.append(int(temp[1]))
        elif 'sort' in temp:
            lst.sort()
        elif 'pop' in temp:
            lst.pop(-1)
        elif 'reverse' in temp:
            lst.reverse()

    for i in nums:
        print(i)