def PowerSetsRecursive(items):  """Use recursive call to return all subsets of items, include empty set"""    if len(items) == 0:    #if the lsit is empty, return the empty list    return [[]]    subsets = []  first_elt = items[0] #first element  rest_list = items[1:]    #Strategy:Get all subsets of rest_list; for each of those subsets, a full subset list  #will contain both the original subset as well as a version of the sebset that contains the first_elt    for partial_sebset in PowerSetsRecursive(rest_list):    subsets.append(partial_sebset)    next_subset = partial_sebset[:] +[first_elt]    subsets.append(next_subset)  return subsets

def PowerSetsRecursive2(items):  # the power set of the empty set has one element, the empty set  result = [[]]  for x in items:    result.extend([subset + [x] for subset in result])  return result 

def PowerSetsBinary(items):   #generate all combination of N items   N = len(items)   #enumerate the 2**N possible combinations   for i in range(2**N):     combo = []     for j in range(N):       #test jth bit of integer i       if(i >> j ) % 2 == 1:         combo.append(items[j])     yield combo