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 examp

Answer 1

In case you do not want to wrap around, the most Pythonic answer would be to use slices. Missing neighbor substituted with None. E.g.:

def nbrs(l, e):
   i = l.index(e)
   return (l[i-1:i] + [None])[0], (l[i+1:i+2] + [None])[0]

This is how the function can work:

>>> nbrs([2,3,4,1], 1)
(4, None)
>>> nbrs([1,2,3], 1)
(None, 2)
>>> nbrs([2,3,4,1,5,6], 1)
(4, 5)
>>> nbrs([], 1)
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 2, in nbrs
ValueError: 1 is not in list