# [Tutor] iterate list items as lvalue

János Juhász janos.juhasz at VELUX.com
Wed Aug 22 15:50:53 CEST 2007

```Dear All,

I would like to thanks for your responds.

Ricardo Aráoz wrote:
Kent Johnson wrote:
> Dave Kuhlman wrote:
>> Consider the following:
>>
>>     >>> array = [1,2,3,4,5]
>>     >>> array2 = array
>>     >>> array = [i * 2 for i in array]
>>     >>> array
>>     [2, 4, 6, 8, 10]
>>     >>> array2
>>     [1, 2, 3, 4, 5]
>>
>> So, did you want array2 to change, or not?
>>
>> Here is a solution that changes the object that both array and
>> array2 refer to:
>>
>>     >>> array = [1, 2, 3, 4, 5]
>>     >>> array2 = array
>>     >>> for idx, item in enumerate(array):
>>         array[idx] = item * 2
>>     >>> array
>>     [2, 4, 6, 8, 10]
>>     >>> array2
>>     [2, 4, 6, 8, 10]
>>
>> Basically, this modifies the list "in place", rather than making a
>> new list from the old one.
>
> Another way to do this is to assign to a slice of array:
>
> array[:] = [ item*2 for item in array ]
>
> Kent
Thanks, hadn't really thought about having a copy of array (guess I'm
too much of a n00b). Really simple and elegant way of solving it though.

I have played the way Kent showed.

>>> array = [1, 2, 3, 4, 5]
>>> array[2] = [item+5 for item in array]
>>> array
[1, 2, [6, 7, 8, 9, 10], 4, 5]

>>> array = [1, 2, 3, 4, 5]
>>> array[2:2] = [item+5 for item in array]
>>> array
[1, 2, 6, 7, 8, 9, 10, 3, 4, 5]

Even more interesting

>>> array = [1, 2, 3, 4, 5]
>>> array[3:2] = ['new','members', 'in', 'the', 'list']
>>> array
[1, 2, 3, 'new', 'members', 'in', 'the', 'list', 4, 5]

Yours sincerely,
Janos Juhasz
```