在Python3中，如何创建数值相等但与其他任何级别的嵌套列表无关的任何级别的嵌套列表

Question

There is a project which I have to implement in python3. However I get stuck with a problem as below.

For the single level list like l=[a,b,c] , a,b,c are not iterable, if want to copy it in content, only use n=l[:] , However, when there is multi-level nested, whose a,b,c are iterable, even if 'pointer' a,b,c are new variable, but their reference are still point at the original position.

a unknown level nested list was transfer as an argument to a function. there will be some operation inside this function to the argument, but I don't want to make any change to the original list object in this function's caller. So i want to copy this object in to a new object.

To make it easy to read, I try some method I wish it can work as below:

>>> a=[1,2,3]
>>> b=[a,a,a]
>>> b
[[1, 2, 3], [1, 2, 3], [1, 2, 3]]
>>> a[1]=10
>>> b
[[1, 10, 3], [1, 10, 3], [1, 10, 3]]
>>> c=list(b)
>>> c
[[1, 10, 3], [1, 10, 3], [1, 10, 3]]
>>> a[1]=20
>>> c
[[1, 20, 3], [1, 20, 3], [1, 20, 3]]
>>> d=b[:][:]
>>> d
[[1, 20, 3], [1, 20, 3], [1, 20, 3]]
>>> a[1]=30
>>> c
[[1, 30, 3], [1, 30, 3], [1, 30, 3]]
>>> d
[[1, 30, 3], [1, 30, 3], [1, 30, 3]]

But all attempt failed.

Are there anyone who have a brief and efficient way to create a new equal but independent object?

Answer 1

I believe the simplest thing would be the following:

b=[list(a),list(a),list(a)]

The problem in your example is that by doing [a,a,a] you do not create new object.

Answer 2

import copy
my_copy = copy.deepcopy(obj_passed_to_me)