On 2/8/2012 9:25 AM, Neil Cerutti wrote:
On 2012-02-08, Mark Lawrence<breamore...@yahoo.co.uk> 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?
Python's indices were designed for these kinds of shenanigans.
def rotated(seq, n):
"""Iterate through all of seq, but starting from index n.
>>> ", ".join(str(n) for n in rotated(range(5), 3))
'3, 4, 0, 1, 2'
"""
i = n - len(seq)
while i< n:
yield seq[i]
i += 1
This is really nice, in the category of "Why didn't I think of that?"
(Probably because I knew the % mod solution from C and never 'updated'!)
if __name__ == "__main__":
import doctest
doctest.testmod()
If you have merely an iterable instead of a sequence, then look
to some of the other clever stuff already posted.
To make a repeating rotator is only a slight adjustment:
k = n - len(seq)
while True:
i = k
while i < n:
yield seq[i]
i += 1
--
Terry Jan Reedy
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