How to make a copy of a list of objects not change when modifying the original list?

Question

Possible Duplicates:
How to clone a list in python?
What is the best way to copy a list in Python?

original_list = [Object1(), Object2(), Object3()]
copy_list = original_list
original_list.pop()

If I remove an object from the original list, how can I keep the copy list from changing as well?

Original List

[<Object.Object instance at 0x00EA29E0>, <Object.Object instance at 0x00EA2DC8>, <Object.Object instance at 0x00EA2EE0>]

Copy List after popping the original list (I want this to equal what is above)

[<Object.Object instance at 0x00EA29E0>, <Object.Object instance at 0x00EA2DC8>]

GreenMatt · Answer 1 · 2011-07-07T18:14:03.663

17

Use copy.deepcopy() for a deep copy:

import copy
copy_list = copy.deepcopy(original_list)

For a shallow copy use copy.copy():

import copy
copy_list = copy.copy(original_list)

or slice with no endpoints specified :

copy_list = original_list[:]

See the copy docs for an explanation about deep & shallow copies.

edited Jul 07 '11 at 18:14

answered Jul 07 '11 at 15:08

GreenMatt

`copy.copy()` is actually shallow copy, `copy.deepcopy()` is deep copy – Jul 07 '11 at 15:46
@Paul Woolcock: Thanks for the catch. I've corrected the answer. – GreenMatt Jul 07 '11 at 18:14
1

Let it be noted that the slice is also a shallow copy, as this was not explicitly said: https://stackoverflow.com/a/19068714/3249197 – starwarswii Mar 07 '18 at 00:42

elricL · Answer 2 · 2011-07-09T03:54:40.387

8

This will work.

import copy
copy_list = copy.copy(original_list)

Also

copy_list = list(original_list)

edited Jul 09 '11 at 03:54

answered Jul 07 '11 at 15:08

elricL

score 1 · Answer 3 · answered Jul 07 '11 at 15:10

Return a deep copy of x.

from copy import deepcopy

original_list = [Object1(), Object2(), Object3()]
copy_list = deepcopy(original_list)
original_list.pop()

But note that slicing will work faster in your case:

copy_list = original_list[:]

3 Answers3