[Tutor] iterate list items as lvalue
Ricardo Aráoz
ricaraoz at gmail.com
Tue Aug 21 00:03:58 CEST 2007
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.
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