[Tutor] circular looping

[Alan Gauld]

"Bala subramanian" <bala.biophysics at gmail.com> wrote


> But here the value of y changes sequentially. I want y to cycle 
> through the
> list something like the following. Is there any function to do such 
> circular
> iteration.
> cycle 1 y's value should be 'N', 'L', 'C', 'M, 'R'  index 1,2,3,4,0 
> of myres
> cycle 2 y's value should be 'L', 'C', 'M, 'R', 'N'  index 2,3,4,0,1 
> ,,
> cycle 3 y's value should be  'C', 'M', 'R', 'N','L' index 3,4,0,1,2 
> ,,

The usual trick to get cyclic indices is to use the mod operator
with the length of the list (and maybe adding a constant)

So

L = "RNLCM"
y = 0  -> (y+1) % len(L) -> 1
y = 1                           -> 2
...
y = 4                           -> 0
y = 5                           -> 1
etc....

Does that help?

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/