Some subset fun.

subsets.py

#!/usr/bin/env python
from itertools import combinations, chain

fun_list = ['a','b','c']

print "\nThe FB way"
def subsets(ins, out=None):
    if out is None:
        out = ['']
    if len(ins) == 0:
        return ['']

    out.extend([x+ins[0] for x in out])
    subsets(ins[1:], out)

    return out

results = subsets(fun_list)
print "\t",sorted(results)


print "\nPython itertools way (probably confusing for non-Pythonistas)"

results = [''.join(fun_list)] # only one combination of all list elements
sequences = [list(chain(combinations(fun_list, n)))
             for (n,l) in enumerate(fun_list)]

results = sum(sequences, results) #sum combines lists, a little cleaner than chain here.
results = [''.join(s) for s in results] # formatting

print "\t",sorted(results)



print "\nA fun way (probably less confusing for non-Pythonistas, but still a bit silly)"

results = []
length = len(fun_list)

for i in range(2**length):
    mask = [((i >> cur_dig) & 1) for cur_dig in range(length-1, -1, -1)]
    results.append(''.join([c for i,c in enumerate(fun_list) if mask[i]]))

print "\t",sorted(results),"\n"