Why does append overwrite the list?

Question

I was trying some questions from hackerrank and came across this question https://www.hackerrank.com/challenges/list-comprehensions/problem

I tried this solution

Answer 1

This line clears the list by deleting all its items. The list stays the same variable (same object), only its contents is modified:

SL[:] = []

Later in the code is this line (in a loop):

L.append(SL)

But SL is the same variable each time. All items in L refer to the same list SL. So when SL is modified, all items in L refer to the new contents of SL.

This can be fixed by creating a new list for each result.