help understanding class or function

Gabriel Genellina gagsl-py2 at
Fri Mar 6 01:13:43 CET 2009

En Thu, 05 Mar 2009 14:43:12 -0200, Vincent Davis  
<vincent at> escribió:

> If I have a list and I what to make changes to it.a = [1,2,3,4,5,6,7,8,9]
> and maybe I want to drop the odd and double the  even numbers and I will
> need to do this repeatedly.
> How is this best done? That is as a function or class. All I know how to  
> do
> is
> def doubleeven(alist):
>     blist = [2*x for x in a if x % 2 ==0]
>    return blist
> then when I am using it I do this
> a = doubleeven(a)
> I what to keep it named "a"
> I am not sure if this is the best way in terms of format or structure. Is
> there a better way.

I don't grasp what you're worried about... Your function does exactly what  
you have specified above, so it's correct. Don't you like the fact that it  
returns a *new* list instead of modifying the original one in-place? You  
may use:

a[:] = doubleeven(a)

Or rewrite the function using a while loop (to avoid having two lists  
alive at the same time), but I would not bother unless there are strong  
reasons (the lists is really huge, or there is very few memory available).

Gabriel Genellina

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