Rotating lists?
Robert Brewer
fumanchu at amor.org
Wed Sep 15 18:26:07 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?
Odd that you would use a slice for only half of it. Did you try:
>>> def rotleft(seq):
... return seq[1:] + seq[:1]
...
>>> rotleft([1,2,3])
[2, 3, 1]
? There are issues with such a simple function (mostly how to deal with
corner cases), but that should be the piece you're missing.
Robert Brewer
MIS
Amor Ministries
fumanchu at amor.org
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