Fining all possible subsets of a given set

Three possible way to create all subsets of a given set is shown below:

1. Using Binary:

lst = ['a', 'b', 'c', 'd', 'e']
def interpret_combination(s):
 s = s[::-1] #reversing the string to match the index positions with the given list
 if not '1' in list(s): # all zeros
  return []
 else:
  indices_of_ones = [i for i, x in enumerate(list(s)) if x == '1'] # find the indices of 1s only
  l = list(s) #convert to list as you can't operate on strings
  for item in indices_of_ones:
   l[item] = lst[item] # replace the one's with the characters on the list
  l = [x for x in l if x != '0'] # replace the zeros
  return ''.join(map(str, l)) # join them to make a string again
all_subsets = []

for i in xrange(2 ** len(lst)): # until 2^(lenght of list)
 l1 = len(str(bin(i))[2:]) # binary representation without the preceding 0b
 l2 = len(lst)
 s = (l2 - l1)*'0' + str(bin(i))[2:] # prepending the zeros in front to make it more readable
 all_subsets.append(interpret_combination(s)) 

print all_subsets

2. Recursive:

def adder(elem, elem_set): # copy elem with each element of elem_set
 exp_lst = []
 for item in elem_set:
  exp_lst.append(elem + item)
 return exp_lst

def all_subsets(s): 
 if len(s) is 0:
  return ''
 elif len(s) is 1:
  return ['', s[0]]
 else:
  return all_subsets(s[:-1]) + adder(s[len(s)-1], all_subsets(s[:-1]))  

print all_subsets(['a','b', 'c', 'd'])  

3. Iterative:

lst = ['a', 'b', 'c', 'd', 'e']
sub_arr = []
sub_arr_tmp = []

for item in lst:
 for elem in sub_arr:
  sub_arr_tmp.append([item + elem])
 sub_arr.append(item)
 if len(sub_arr_tmp) is 0:
  sub_arr.append('')
 else:
   for e in sub_arr_tmp:
    if(isinstance(e, list)):
     sub_arr.append(e[0])
 del sub_arr_tmp[:]

print set(sub_arr)
print len(set(sub_arr))