[Python-Dev] Retrieve an arbitrary element from a set without removing it (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Fri Oct 30 16:35:33 CET 2009

Steven D'Aprano <steve pearwood.info> writes:

If you can think of any other way to efficiently cycle over the elements in a set, I'm all for it :)

How about "for x in s"?

Or if you want to cycle:

s = set('abc') it = itertools.cycle(s) next(it) 'a' next(it) 'c' next(it) 'b' next(it) 'a'

Or if you don't want the overhead of itertools.cycle() keeping a copy of the set's elements:

s = set('abc') it = itertools.chain.fromiterable(itertools.cycle([s])) next(it) 'a' next(it) 'c' next(it) 'b' next(it) 'a' next(it) 'c' next(it) 'b'

I can't say I've seen one in any other languages, but Wikipedia lists "pick" as a fundamental set operation:

pick(S): returns an arbitrary element of S.

Well, it's an arbitrary element. It isn't specified that it will try to return different results in a row to satisfy the developer's aesthetical preferences...

This page claims that Icon has an operator that returns a random element of a set:

? set( [1, 2, 3, 4, 5] )

random != arbitrary != weak-guaranteedly distinct

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