Rotating lists?

Jim Sizelove sizelji at insightbb.com
Thu Sep 16 15:19:53 CEST 2004


Thorsten Kampe wrote:
> 
> def rotate(seq,
>            offset):
>     """ shift seq to the left by offset, with the elements shifted off the
>     beginning inserted back at the end """
>     return seq[offset:] + seq[:offset]


You can also use a generator function:

def rotator(seq, offset=1):
     while True:
         yield seq
         seq = seq[offset:] + seq[:offset]

T = rotator(range(5))
T.next()
[0, 1, 2, 3, 4]
T.next()
[1, 2, 3, 4, 0]
T.next()
[2, 3, 4, 0, 1]

You can rotate to the right using a negative offset:
L = rotator( range(5), -1 )
L.next()
[0, 1, 2, 3, 4]
L.next()
[4, 0, 1, 2, 3]
L.next()
[3, 4, 0, 1, 2]



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