[Python-Dev] Retrieve an arbitrary element from a set without removing it
John Arbash Meinel
john.arbash.meinel at gmail.com
Fri Oct 23 22:11:57 CEST 2009
Terry Reedy wrote:
> John Arbash Meinel wrote:
>> So 'for x in s: break' is about 2x faster than next(iter(s)) and 3x
>> faster than (iter(s).next()).
>> I was pretty surprised that it was 30% faster than "for x in s: pass". I
>> assume it has something to do with a potential "else:" statement?
> for x in s: pass
> iterates through *all* the elements in s and leaves x bound to the
> arbritrary *last* one instead of the arbitrary *first* one. For a large
> set, this would be a lot slower, not just a little.
> fwiw, I think the use case for this is sufficiently rare that it does
> not need a separate method just for this purpose.
The point of my test was that it was a set with a *single* item, and
'break' was 30% faster than 'pass'. Which was surprising. Certainly the
difference is huge if there are 10k items in the set.
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