# from python.org, http://docs.python.org/library/itertools.html
# the equivalent for itertools.combinations in a version of Python
# less than 2.6
def combinations(iterable, r):
# combinations('ABCD', 2) --> AB AC AD BC BD CD
# combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
if r > n:
return
indices = range(r)
yield tuple(pool[i] for i in indices)
while True:
for i in reversed(range(r)):
if indices[i] != i + n - r:
break
else:
return
indices[i] += 1
for j in range(i+1, r):
indices[j] = indices[j-1] + 1
yield tuple(pool[i] for i in indices)
# essentially 5 choose 2 combinations from a list
# since it is a generator, you have to explicitly iterate
# through all combinations
for x in combinations(range(5),2):
print x