Terry Reedy wrote:
> 3. Process the items of an iterable in pairs.
>
> items = iter(iterable)
> for first in items:
> second = next(items)
> <process first and second>
>
> This time, StopIteration is raised for an odd number of items. Catch and
> process as desired. One possibility is to raise ValueError("Iterable
> must have an even number of items").
Another way is zip-based iteration:
(a) silently drop the odd item
items = iter(iterable)
for first, second in zip(items, items): # itertools.izip in 2.x
...
(b) add a fill value
for first, second in itertools.zip_longest(items, items):
...
(c) raise an exception
Unfortunately there is no zip_exc() that guarantees that all iterables are
of the same "length", but I've written a recipe some time ago
http://code.activestate.com/recipes/497006-zip_exc-a-lazy-zip-that-ensures-
that-all-iterables/
that achieves near-C speed.
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