On 27/05/2014 13:44, Tal Einat wrote:
On Tue, May 27, 2014 at 2:45 PM, Michael Urman <mur...@gmail.com> wrote:
On Tue, May 27, 2014 at 4:05 AM, Chris Angelico <ros...@gmail.com> wrote:
On Tue, May 27, 2014 at 6:58 PM, Serhiy Storchaka <storch...@gmail.com> wrote:
26.05.14 10:59, raymond.hettinger написав(ла):
+ result = [(elem, i) for i, elem in zip(range(n), it)]
Perhaps it is worth to add simple comment explaining why this is not
equivalent to just list(zip(it, range(n))). Otherwise it can be
unintentionally "optimized" in future.
Where is the difference? I'm very much puzzled now. My first thought
was based on differing-length iterables in zip, but the docs say it
stops at the shortest of its args.
Due to how zip stops, it leaves the longer iterable in different places:
it = iter(string.ascii_letters); list(zip(range(3), it)); next(it)
[(0, 'a'), (1, 'b'), (2, 'c')]
'd'
it = iter(string.ascii_letters); list(zip(it, range(3))); next(it)
[('a', 0), ('b', 1), ('c', 2)]
'e'
This seems like a potentially nasty gotcha, but I'm unclear what real
use cases would be impacted.
If that's the issue, a comment explaining it should definitely be added.
+1. FWIW I couldn't see the difference between the 2 codings. I was
relieved to see that the zip() doc says
"The left-to-right evaluation order of the iterables is guaranteed."
Even so, I don't think the reliance on this is obvious.
Rob Cliffe
We could also use islice(enumerate(it), n)) to avoid the confusion.
- Tal
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