求一个集合所有子集的Python实现

方法一：回归实现

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])