Rotating lists?
Irmen de Jong
irmen at -nospam-remove-this-xs4all.nl
Wed Sep 15 18:53:07 EDT 2004
Ivan Voras wrote:
> I need to transform this:
>
> [1,2,3]
>
> into this:
>
> [2,3,1]
>
> (a left-rotation. Actually, any rotation will do).
>
> I tried:
>
> a = a[1:] + a[0]
>
> which doesn't work because there's no __add__ between a list and
> integer, and:
>
> a = a[1:].append(a[0])
>
> but it doesn't work, since append returns None :( Right now, I'm doing
> it with a temporary variable and it looks ugly - is there an elegant way
> of doing it?
>
This smells like a use-case for itertools.cycle:
>>> import itertools
>>> c=itertools.cycle( [1,2,3] )
>>> c.next()
1
>>> c.next()
2
>>> c.next()
3
>>> c.next()
1
>>> c.next()
2
... or is this not what you need to rotate your lists for?
--Irmen de Jong
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