random.shuffle question

[Erik Max Francis]

dsavitsk wrote:

> why does this not work to shuffle part of a list?
> 
> >>> l = [1,2,3,4,5,6,7,8,9]
> >>> random.shuffle(l[4:8])
> >>> print l
> [1, 2, 3, 4, 5, 6, 7, 8, 9]
> 
> and more importantly, is there a better way to do this?

random.shuffle shuffles the list you hand it, and when you create a
slice of a list, that sublist is separate from the original list.  So
you're creating a new sublist, shuffling it, and then tossing it away.

You could simply chop up the list, shuffle the part that you want, and
then reassemble it:

>>> import random
>>> l = [1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> lBegin = l[:4]
>>> lMiddle = l[4:8]
>>> lEnd = l[8:]
>>> random.shuffle(lMiddle)
>>> l2 = lBegin + lMiddle + lEnd
>>> l2
[1, 2, 3, 4, 6, 5, 8, 7, 9]


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