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

def pairwise(iterable):
    """s -> (s0,s1), (s1,s2), (s2, s3), ...
    see http://docs.python.org/library/itertools.html
    """
    a, b = itertools.tee(iterable)
    b.next()
    return itertools.izip(a, b)

EDIT moved doc string into the function