python - Pythonic Circular List

Question

Say I have a list,

l = [1, 2, 3, 4, 5, 6, 7, 8]

I want to grab the index of an arbitrary element and the values of its neighbors. For example,

i = l.index(n)
j = l[i-1]
k = l[i+1]

However, for the edge case when i == len(l) - 1 this fails. So I thought I'd just wrap it around,

if i == len(l) - 1:
    k = l[0]
else:
    k = l[i+1]

Is there a pythonic way to do this?

Answer 1

You could use the modulo operator!

i = len(l) - 1
jIndex = (i - 1) % len(l)
kIndex = (i + 1) % len(l)

j = l[jIndex]
k = l[kIndex]

Or, to be less verbose:

k = l[(i + 1) % len(l)]