I want to create an undo() function that undoes the last operation in python, so I just deepcopied the list before any modifications were made during whatever function to another list (I made a bootleg deepcopy by myself), called undolist, and then when I call undo() I just pop the last element from the undolist

I know there are other more efficient ways of doing this, but given my time constraints and my mental in-capabilities I don't think I could turn this in.

However, it doesn't work. I am going to post an example of how I implemented the undo function and the bootleg deepcopy on a random function, since the code itself is super long and in another language

I hope I've made myself clear enough, if there are any misunderstandings I'll edit the post.

main_list = [list of lists that have elements in them]


def bootleg_deepcopy(main_list):
    new_list = []
    for x in main_list:
        nx = x[:]
        new_list.append(nx)
    return new_list
    
    
def delete_elements(main_list,user_input,undolist):
    #function that deletes elements from the list if a condition isn't met
    undolist.append(bootleg_deepcopy(main_list))
    main_list[:] = [element for element in main_list if not function_that_checks_something(whatever,something)]
    return main_list


def undo(main_list,undolist):
    try:
        main_list = undolist.pop()
    except Exception as ex:
        print(ex)
    return main_list

CodePudding user response：

Your undo simply returns a new reference to main_list. Your delete_elements method overwrites the main_list in-place (main_list[:] = ...). I assume you want the same behavior in your undo action so that all places that hold references to main_list are updated automatically.

CodePudding user response：

The solution was to use the slice operator(?) in the undo() function. I've edited it so that it includes the right code.

def undo(main_list,undolist):
    try:
        main_list[:] = undolist.pop()
    except Exception as ex:
        print(ex)
    return main_list