"Mensanator" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] On Jun 6, 1:44 am, "Terry Reedy" <[EMAIL PROTECTED]> wrote: > "Mensanator" <[EMAIL PROTECTED]> wrote in message > > news:[EMAIL PROTECTED] > | On Jun 5, 10:42?pm, John Salerno <[EMAIL PROTECTED]> wrote: > | > Is it possible to write a list comprehension for this so as to > produce > a > | > list of two-item tuples? > | > > | > base_scores = range(8, 19) > | > score_costs = [0, 1, 1, 1, 1, 1, 1, 2, 2, 3, 3] > | > print zip(base_scores, score_costs) > | > > | > I can't think of how the structure of the list comprehension would > work > | > in this case, because it seems to require iteration over two separate > | > sequences to produce each item in the tuple. > > Which is exactly the purpose of zip, or its specialization enumerate!
Aren't you overlooking the fact that zip() truncates the output to the shorter length iterable? ========================= <message does not quote correctly> <me> No. ========================= And since the OP foolishly hardcoded his range bounds, zip(base_scores,score_cost) will silently return the wrong answer if the base_count list grows. ============ <me> So, to future proof his code he should better use zip(itertools.count(8), score_costs). I consider this better than using enumerate to make the wrong pairing (with itertools.count(0)) and then correcting the mistake. ==================== Surely enumerate() wasn't added to Python with no intention of ever being used. ======================== <me> Of course not, so why suggest that is was? However, it was intended for the most common case when one wants to pair items with counts beginning with 0. ================================= > Of course, enumerate(iterable) is just a facade over > zip(itertools.count(), > iterable) But if all I'm using itertools for is the count() function, why would I go to the trouble of importing it when I can simply use enumerate()? ==================================== <me>I have no idea. The purpose of enumerate is to be easy. But it is not so easy when it gives the wrong pairings. =================================== Is it a couple orders of magnitude faster? ================================= <me> Perhaps you do not understand 'facade' - the front part or face of something that you see. I was saying that enumerate is a face on a room containing zip and itertools.count, or the equivalent code thereof. Therefore, enumerate is an easy way to do a particular zip, not an alternative to zip. And there should be no significant performance difference, certainly for long sequences which make the additional lookups irrelevant. tjr -- http://mail.python.org/mailman/listinfo/python-list
