Changing a Value in List of lists

[Rishabh Dixit]

Hi,

I got it :). We should create a new list every time before adding to a list
of list so that instead repeating the reference a new reference generated
every time.

>>> mat=[[0]*5 for i in range(5)]
>>> mat[1][2]+=1
>>> mat
[[0, 0, 0, 0, 0], [0, 0, 1, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0,
0, 0, 0]]

This worked for me!! Thanx :)

On Sun, Sep 2, 2012 at 4:30 PM, Rishabh Dixit <rishabhdixit11 at gmail.com>wrote:

> Hi Chris,
>
> Thanks for your reply. I tried this -
>
> >>> ls=[0 for i in range(5)]
> >>> mat=[ls for i in range(5)]
> >>> mat[1][2]+=1
> >>> mat
> [[0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0, 0, 1, 0, 0], [0,
> 0, 1, 0, 0]]
>
> I guess here also the same issue is there as ls refers to one list that is
> being repeated through mat and change in one causes change in others also.
>
> Is there any solution to change all elements independently.
>
>
>
> On Sun, Sep 2, 2012 at 3:14 PM, Rishabh Dixit <rishabhdixit11 at gmail.com>wrote:
>
>>
>> Hi all,
>>
>> I have a doubt regarding how the list work in following case-
>>
>> >>> ls=[[0]*5]*5
>> >>> ls[1][1]+=1
>> >>> ls
>> [[0, 1, 0, 0, 0], [0, 1, 0, 0, 0], [0, 1, 0, 0, 0], [0, 1, 0, 0, 0], [0,
>> 1, 0, 0, 0]]
>>
>>
>> Here, according to me only one value in ls should be incremented but it
>> is increasing 1 value in all the lists of ls. Why??
>> --
>> Regards,
>> Rishabh Dixit
>> MSc.(Tech) Information Systems,
>> BITS Pilani
>>
>>
>
>
> --
> Regards,
> Rishabh Dixit
> MSc.(Tech) Information Systems,
> BITS Pilani
>
>


-- 
Regards,
Rishabh Dixit
MSc.(Tech) Information Systems,
BITS Pilani
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