def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = itt.tee(iterable)
    next(b, None)
    return zip(a, b)
def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = itt.tee(iterable)
    next(b, None)
    return zip(a, b)
s -> (s0,s1), (s1,s2), (s2, s3), ...