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

Question

Suppose the following:

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

How do I get a value (any value) out of s without doing s.pop()

Answer 1

To provide some timing figures behind the different approaches, consider the following code. The get() is my custom addition to Python's setobject.c, being just a pop() without removing the element.

from timeit import *

stats = ["for i in xrange(1000): iter(s).next()   ",
         "for i in xrange(1000): \n\tfor x in s: \n\t\tbreak",
         "for i in xrange(1000): s.add(s.pop())   ",
         "for i in xrange(1000): s.get()          "]

for stat in stats:
    t = Timer(stat, setup="s=set(range(100))")
    try:
        print "Time for %s:\t %f"%(stat, t.timeit(number=1000))
    except:
        t.print_exc()

The output is:

$ ./test_get.py
Time for for i in xrange(1000): iter(s).next()   :       0.433080
Time for for i in xrange(1000):
        for x in s:
                break:   0.148695
Time for for i in xrange(1000): s.add(s.pop())   :       0.317418
Time for for i in xrange(1000): s.get()          :       0.146673

This means that the for/break solution is the fastest (sometimes faster than the custom get() solution).