How to retrieve an element from a set without removing it?

python set
Daren Thomas picture Daren Thomas · Sep 12, 2008 · Viewed 488.7k times · Source

Suppose the following:

>>> s = set([1, 2, 3])

How do I get a value (any value) out of s without doing s.pop()? I want to leave the item in the set until I am sure I can remove it - something I can only be sure of after an asynchronous call to another host.

Quick and dirty:

>>> elem = s.pop()
>>> s.add(elem)

But do you know of a better way? Ideally in constant time.

Answer

Blair Conrad picture Blair Conrad · Sep 12, 2008

Two options that don't require copying the whole set:

for e in s:
    break
# e is now an element from s

Or...

e = next(iter(s))

But in general, sets don't support indexing or slicing.

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