求一个集合所有子集的Python实现

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