# [Tutor] cyclically rotate a seq

kevin parks kp8 at mac.com
Fri Mar 11 06:43:59 CET 2005

```Hi folks,

I am trying to cyclically rotate a seq until it reached the beginning
stage again.
I would like to be able to rotate in both directions and using any
arbitrary interval.
I think that I have this correct, but would be happy for someone to
check it and also
i am interested in any improvements or enhancements. It is important
that this
work correctly or the whole rest of my code will be in barf *^-^* hee
hee. So
any help would be appreciated.

#!/usr/bin/env python

import sys
import random

# cyclically rotate a sequence
# -- --------------------------------------------------------
# should work on any sequence type
# should work with any hop(n) interval
# should also work in both directions (left or right)
# -- --------------------------------------------------------

def rotate(seq, n=1):
if len(seq) == 0:
return seq
# Normalize n, using modulo - even works for negative n
n = n % len(seq)
return seq[n:] + seq[:n]

def test():
start = 1
x = [7, 2, 1, 0, 11, 6, 5, 4]
print; print x; print '--' * 8
for i in range(len(x)):
out = rotate(x, start)
print out
start = start + 1

if __name__ == "__main__":
test()

# -------- EOF --------

```