不是一种有效的方法，而是一种棘手的方法：

def listAllSubset(remaining = set(),used = set()):
    remaining.discard
    used.discard
    ...

isinstance是权威的，重点在代码的最后一行，

这是代码

def listAllSubset(remaining = set(),used = set()):
    assert(isinstance(remaining,set))
    assert(isinstance(used,set))

    if (len(remaining) == 0):
        print(used)
    else:
        element = remaining.pop()    # OK: element will be None
        listAllSubset(remaining,used)   # OK: remaining == used == set() 
        listAllSubset(remaining,used.add(element))    # Error: used.add(element) will return None,and the None will give to keyword argument "used",then "assert" will raise a AssertionError.

if __name__ == "__main__":
    listAllSubset()

好吧， 最后一行代码listAllSubset(remaining,used.add(element))与listAllSubset(set(),None相等）， 然后assert(isinstance(used,set))会引发AssertionError

只看这段代码

used = set()
flag = used.add('_')
print(flag)    # print value of flag

  

没有

已更改

我更改了代码，但它可以满足您的需求，

def listAllSubset(remaining = set(),set))

    if (len(remaining) == 0):
        print(used)
    else:
        element = remaining.pop()
        listAllSubset(remaining,used)
        used.add(element)
        listAllSubset(remaining,used)

请原谅我的英语不好，英语太难了！