Why value of input list is getting changed?

Question

As I don't know what title should be given to my this confusion so I'm putting it just a doubt

a = [1,2,3,4,5]
b = a 

for i in range(len(a)):
    c = (i - 4)
    print(a)
    print(b)
    b[c] = a[i]
    print(a)
    print(b)

output

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[1, 1, 3, 4, 5]
[1, 1, 3, 4, 5]
[1, 1, 3, 4, 5]
[1, 1, 3, 4, 5]
[1, 1, 1, 4, 5]
[1, 1, 1, 4, 5]
...

why values of list a is getting in each step of loop?

Your code does not run as `b` is not defined. Please can you check / update. — jpp, Jun 01 '18 at 14:19
Change ```b = a``` to ```b = list(a)```. The way you did just make ```a``` and ```b``` just point to the same array. — accdias, Jun 01 '18 at 14:23

Robᵩ · Answer 1 · 2018-06-01T14:26:50.150

3

Your problem lies in this line:

b = a

This doesn't do what you think it does. In particular, it does not make a copy of a. After the assignment, both b and a refer to the same object. Thus, any change to b is reflected in a also.

One way to force a shall copy is to use the slice syntax:

b = a[:]

edited Jun 01 '18 at 14:26

answered Jun 01 '18 at 14:22

Robᵩ

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Thanx man, doubt cleared – Sudhir Kumar Shahu Jun 01 '18 at 14:24
But please study the duplicate questions. The answers there are much more revealing than my answer here. – Robᵩ Jun 01 '18 at 14:26

Why value of input list is getting changed?

1 Answers1