On Fri, 23 Oct 2009 08:32:45 pm Willi Richert wrote: > Hi, > > recently I wrote an algorithm, in which very often I had to get an > arbitrary element from a set without removing it. > > Three possibilities came to mind: ... > Of course, the third should be the fastest.
If you need one or more items chosen randomly without replacement, use a list: L = list(some_set) x = random.choice(L) If you don't need a randomly chosen item, merely an arbitrary item, you can still use a list but avoid the call to random.choice: x = list(some_set)[0] > It nevertheless goes > through all the iterator creation stuff, which costs some time. I > wondered, why the builtin set does not provide a more direct and > efficient way for retrieving some element without removing it. Is > there any reason for this? I can see it being useful to iterate over the entire set, without removing anything. I can see it being useful to pop an arbitrary item, and remove it. But I can't see the use for retrieving an arbitrary item, leaving it in the set. What do you use this for? > I imagine something like > > x = some_set.get() > > or > > x = some_set.pop(False) > > and am thinking about providing a patch against setobject.c > (preferring the .get() solution being a stripped down pop()). -1 on .pop(flag) +0 on .get() -- Steven D'Aprano _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
