writing a deepcopy without using deepcopy

November 22, 2023

So I need to make a deepcopy of a nested list but without using the import copy. I have a sepereate function that outputs Board
Board = [['B', 'B', 'B', 'B', 'B'], ['B', 'B', 'B', 'B', 'B'], ['B', 'B', '', 'W', 'W'], ['W', 'W', 'W', 'W', 'W'], ['W', 'W', 'W', 'W', 'W'], 0]

So I thought of doing this to make a deepcopy using for loop:

def copy(b: Board) -> Board:
    if isinstance(b, list):
        return [copy(item) for item in b]
    else:
        return b

But when doing this I think I just returns b without making a deepcopy, since the 0 at the end is an integer?
Am I also correct in thinking that to test if I made a correct deepcopy I can do the following to confirm:

copy == Board 
True 
copy is Board
False

when returning copy i get the following:
[['B', 'B', 'B', 'B', 'B'], ['B', 'B', 'B', 'B', 'B'], ['B', 'B', '', 'W', 'W'], ['W', 'W', 'W', 'W', 'W'], ['W', 'W', 'W', 'W', 'W'], 0]
but when trying to test with "==" and "is" I get:

copy == make_Board
False
copy is make_Board
False

>Solution :

To make a copy of the Board you can use next example:

Board = [
    ["B", "B", "B", "B", "B"],
    ["B", "B", "B", "B", "B"],
    ["B", "B", "", "W", "W"],
    ["W", "W", "W", "W", "W"],
    ["W", "W", "W", "W", "W"],
    0,
]


def copy_board(b):
    return [item[:] if isinstance(item, list) else item for item in b]


new_Board = copy_board(Board)
new_Board[0][0] = "XXX"

print(Board)
print(new_Board)

Prints:

[
    ["B", "B", "B", "B", "B"],
    ["B", "B", "B", "B", "B"],
    ["B", "B", "", "W", "W"],
    ["W", "W", "W", "W", "W"],
    ["W", "W", "W", "W", "W"],
    0,
]

[
    ["XXX", "B", "B", "B", "B"],
    ["B", "B", "B", "B", "B"],
    ["B", "B", "", "W", "W"],
    ["W", "W", "W", "W", "W"],
    ["W", "W", "W", "W", "W"],
    0,
]