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Raymond's point about opaqueness is well-taken, since the
given partitioning behaviour in the example was actually
what was intended (I was part of the relevant c.l.p discussion).

For future reference, the reliable approach is to use a
generator function instead:

from itertools import islice
def partition(iterable, part_len):
    itr = iter(iterable)
    while 1:
        yield tuple(islice(itr, part_len))