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

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

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

e = next(iter(s))

>>> s = set([1, 2, 3])
>>> list(s)[0]
1

from timeit import *

stats = ["for i in xrange(1000): iter(s).next()   ",
         "for i in xrange(1000): ntfor x in s: nttbreak",
         "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()

$ ./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

>>> import random
>>> s = set([1,2,3])
>>> random.sample(s, 1)
[2]

>>> list(set(range(10))) == range(10)
True

>>> lst = list(s) # once, O(len(s))?
...
>>> e = random.sample(lst, 1)[0] # constant time

from timeit import Timer

stats = [
    "for i in range(1000): ntfor x in s: nttbreak",
    "for i in range(1000): next(iter(s))",
    "for i in range(1000): s.add(s.pop())",
    "for i in range(1000): list(s)[0]",
    "for i in range(1000): random.sample(s, 1)",
]

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

$ ./test_get.py
Time for for i in range(1000):
    for x in s:
        break:   0.249871
Time for for i in range(1000): next(iter(s)):    0.526266
Time for for i in range(1000): s.add(s.pop()):   0.658832
Time for for i in range(1000): list(s)[0]:   4.117106
Time for for i in range(1000): random.sample(s, 1):  21.851104

def anyitem(iterable):
    try:
        return iter(iterable).next()
    except StopIteration:
        return None

from timeit import *

stats = ["for i in range(1000): next(iter(s))",
         "for i in range(1000): ntfor x in s: nttbreak",
         "for i in range(1000): s.add(s.pop())"]

for stat in stats:
    t = Timer(stat, setup="s=set(range(100000))")
    try:
        print("Time for %s:t %f"%(stat, t.timeit(number=1000)))
    except:
        t.print_exc()

Time for for i in range(1000): next(iter(s)):    0.205888
Time for for i in range(1000):
    for x in s:
        break:                                   0.083397
Time for for i in range(1000): s.add(s.pop()):   0.226570

from timeit import *

stats = ["while s:nta = next(iter(s))nts.remove(a)",
         "while s:ntfor x in s: breaknts.remove(x)",
         "while s:ntx=s.pop()nts.add(x)nts.remove(x)"]

for stat in stats:
    t = Timer(stat, setup="s=set(range(100000))")
    try:
        print("Time for %s:t %f"%(stat, t.timeit(number=1000)))
    except:
        t.print_exc()

Time for while s:
    a = next(iter(s))
    s.remove(a):             2.938494
Time for while s:
    for x in s: break
    s.remove(x):             2.728367
Time for while s:
    x=s.pop()
    s.add(x)
    s.remove(x):             0.030272

e,*_=s

[*s][0]

poor_man_set = {}
poor_man_set[1] = None
poor_man_set[2] = None
poor_man_set[3] = None
...

keys = poor_man_set.keys()
print "Some key = %s" % keys[0]

poor_man_set = {}
poor_man_set[1] = None
poor_man_set[2] = None
poor_man_set[3] = None
poor_man_set = poor_man_set.keys()