Python deepcopy to while statement

[hito koto]

Hi, all

I want to make the function use while statement,and  without a deepcopy functions.

this is my use deepcopy  function　ｃorrect　codes, So, how can i to do a different way  and use while statement:

def foo(x):
    if not isinstance(x, list):
        return x
    return [foo(y) for y in x]