If you don't care about the order of the results, you can use a Gray

code (

http://en.wikipedia.org/wiki/Gray_code): this has the advantage

of only adding or removing a single element to get from one subset to

the next.

def powerset(s):

d = dict(zip(

(1<<i for i in range(len(s))),

(set([e]) for e in s)

))

subset = set()

yield subset

for i in range(1, 1<<len(s)):

subset = subset ^ d[i & -i]

yield subset

>>> list(powerset('abc'))
[set([]), set(['a']), set(['a', 'b']), set(['b']), set(['c', 'b']),

set(['a', 'c', 'b']), set(['a', 'c']), set(['c'])]

If you're using the subsets as they appear and don't need to store

them all at once, then it's significantly faster (on my machine) if

you replace the line subset = subset ^ d[i & -i] with an in-place

update: subset ^= d[i & -i].

Mark