Pairwise circular Python 'for' loop

Question

Is there a nice Pythonic way to loop over a list, retuning a pair of elements? The last element should be paired with the first.

So for instance, if I have the list [1, 2, 3], I would like to get the following pairs:

• 1 - 2
• 2 - 3
• 3 - 1

Answer 1

A Pythonic way to access a list pairwise is: zip(L, L[1:]). To connect the last item to the first one:

>>> L = [1, 2, 3] >>> zip(L, L[1:] + L[:1]) [(1, 2), (2, 3), (3, 1)] 

Answer 2

I would use a deque with zip to achieve this.

>>> from collections import deque >>> >>> l = [1,2,3] >>> d = deque(l) >>> d.rotate(-1) >>> zip(l, d) [(1, 2), (2, 3), (3, 1)]