def chunks(iterable, size, longest=True, fillwith=None):
    iterable = iter(iterable)
    while True:
        ret = ()
        try:
            for x in xrange(size):
                ret += (iterable.next(), )
        except StopIteration:
            if longest and ret:
                while len(ret) < size:
                    ret += (fillwith, )
                yield ret
            return
        yield ret