Cycle around a sequence

Peter Otten __peter__ at web.de
Thu Feb 9 09:36:30 CET 2012


Mark Lawrence wrote:

> I'm looking at a way of cycling around a sequence i.e. starting at some
> given location in the middle of a sequence and running to the end before
> coming back to the beginning and running to the start place.  About the
> best I could come up with is the following, any better ideas for some
> definition of better?

You could use a deque instead of a list and .rotate() that:

>>> from collections import deque
>>> d = deque(range(10))
>>> d.rotate(-4)
>>> d
deque([4, 5, 6, 7, 8, 9, 0, 1, 2, 3])

> 
> PythonWin 2.7.2 (default, Jun 12 2011, 15:08:59) [MSC v.1500 32 bit
> (Intel)] on win32.
> Portions Copyright 1994-2008 Mark Hammond - see 'Help/About PythonWin'
> for further copyright information.
>  >>> from itertools import chain
>  >>> a=range(10)
>  >>> g = chain((a[i] for i in xrange(4, 10, 1)), (a[i] for i in
>  >>> xrange(4))) for x in g: print x,
> ...
> 4 5 6 7 8 9 0 1 2 3
>  >>>





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