[Tutor] A shorter way to initialize a list?

[Prasad, Ramit]

From: tutor-bounces+ramit.prasad=jpmorgan.com at python.org [mailto:tutor-bounces+ramit.prasad=jpmorgan.com at python.org] On Behalf Of Kaixi Luo
Sent: Tuesday, December 13, 2011 2:39 PM
To: tutor at python.org
Subject: [Tutor] A shorter way to initialize a list?

Hello,

I want to create a list of lists of lists (listB) from a list of lists (listA). Below there's a snippet of my code:

list1 = [[] for i in range(9)]

# some code here...

listA = [[] for i in range(3)]
count = 0
for i in range(3):
    for j in range(3):
        listB[i].append(listA[count])
        count+=1

My question is: is there any alternative way I can initialize listB without resorting to using 2 loops? 

========================================

I do not understand the double loop. listA is only of length 3, so it 
will fail as soon as count=3 (when i=1,j=0). 

listA only has 3 sublists and listB has 9. I am not sure how you are trying to 
append them and frankly I can guess half a dozen various reasons that seem
equally plausible to me. If they are both supposed to be the same size then you
should check copy.deepcopy which will make new objects (versus just references)
for every sublist (or any object for that matter ) in the original list. 
Otherwise you will need to be aware that appending a sublist from 
listA to listB will mean that if you modify a sublist in listA it 
will modify the corresponding sublist of listB and vice-versa.

If you clarified what you are trying to do (or better yet gave sample
results), I could help you better.

Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423

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