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[Python-Dev] Retrieve an arbitrary element from a set without removing it

Willi Richert w.richert at gmx.net
Fri Oct 23 11:32:45 CEST 2009 
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:

1. 
x = some_set.pop()
some_set.add(x)

2. 
for x in some_set: 
	break

3.
x = iter(some_set).next()


Of course, the third should be the fastest. 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 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()).

Before, I would like to know whether I have overlooked something or whether 
this can be done in an already existing way.

Thanks,
wr
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