How to stop old list getting updated when updating new list in Python

Asked Jul 26 '20 at 13:12

Active Jul 26 '20 at 13:12

Viewed 29 times

I am new to Python, I am trying to solve following problem.

Given a list, find even numbers and replace it with 2 of the same.

Sample input:

[2,5,4,0]

Sample output:

[2,2,5,4,4,0,0]

My solution:

l2 = [2,5,4,0]
def dupEven(l2):
    l3 = l2
    for i in l2:
        if i % 2 == 0:
            l3.insert(l3[i],i)

If I try to run the program, it is going in loop as it seems the old list (l1) keeps getting updated whenever the new list getting updated (l2).

How can I stop the old list getting updated when I update the new list in Python?

asked Jul 26 '20 at 13:12

smc

1

You don't have an old list and a new list. You have two references to one list. – user2357112 Jul 26 '20 at 13:14
(Also, you're inserting elements at the wrong indices.) – user2357112 Jul 26 '20 at 13:15
Ah, yes, I guess when I update the l3, the indices will change :(. Thanks. – smc Jul 26 '20 at 13:16
That, and `l3[i]` is the wrong index from the start. – user2357112 Jul 26 '20 at 13:17
Sorry. from the start? My expectation is `l3[i]` is basically as same as `l2[i]` (at least in the start). Isn't? – smc Jul 26 '20 at 13:21
It is, but `l2[i]` is the wrong index. For example, on the first iteration, `i` is `2` and `l2[i]` is `4`, so you're trying to insert at index 4 instead of 0. – user2357112 Jul 26 '20 at 13:25

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