Most pythonic way to get the previous element

Question

I would like an enumerate-like functional on iterators which yields the pair (previous_element, current_element). That is, given that iter

Answer 1

To put more itertools on the table:

from itertools import tee, izip, chain

def tee_zip(iterable):
   a, b = tee(iterable)
   return izip(chain([None], a), b)