On 9/11/2011 9:41 AM, Peter Otten wrote:
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
...
In practice, I would use this rather than the loop above. However, I
wanted to introduce the idea then used in the intermittent pairing of
surrogates.
(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.
Interesting. It took a moment to see the general idea. For some reason,
you timeit examples in the comment now all have "data = [range(1000)]3",
missing '*'.
--
Terry Jan Reedy
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