changing values in copied list

Asked Aug 04 '17 at 09:33

Active Aug 04 '17 at 09:40

Viewed 49 times

I have a question about how changing values in copied(?) lists can affect the original one.

An Example:

a = [1, 2, [3,4]]
b = list(a)

b.append(100)
b 
[1,2,[3,4],100]
a 
[1,2,[3,4]] 

b[2][0] = -100
b 
[1,2,[-100,4],100] 
a
[1,2,[-100,4]] 

b[0] = 3
b 
[3,2,[-100,4],100] and
a
[1,2,[-100,4]]

Why sometimes changing or adding values on list(b) doesn't affect list(a) and sometimes it does affect list(a)?

edited Aug 04 '17 at 09:40

slartidan

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asked Aug 04 '17 at 09:33

오정훈

first of all format your question. I, personally, can't understand what your code is doing. – Chiheb Nexus Aug 04 '17 at 09:35
1

This is just copying the reference. You might want to look at https://stackoverflow.com/questions/19951816/python-changes-to-my-copy-variable-affect-the-original-variable – Pansul Bhatt Aug 04 '17 at 09:35
1

`list(a)` or `a[:]` returns a shallow copy, i.e only the outer container changes(inner objects remain the same) – Ashwini Chaudhary Aug 04 '17 at 09:36
use `copy.deepcopy(a)` – dabadaba Aug 04 '17 at 09:37

changing values in copied list

0 Answers0