列出一個列表中所有子集合

def powerset(iterable):
    # modified from itertools.combinations example:
    # https://docs.python.org/ja/3/library/itertools.html#itertools.combinations
    # powerset("ABCD") --> _ A B C D AB AC AD BC BD CD ABC ABD ACD BCD ABCD
    # powerset(range(4)) --> _ 0 1 2 3 01 02 03 12 13 23 012 013 023 123 0123

    pool = tuple(iterable)
    n = len(pool)
    for r in range(n + 1):
        indices = list(range(r))
        yield list(pool[i] for i in indices)
        while True:
            for i in reversed(range(r)):
                if indices[i] != i + n - r:
                    break
            else:
                break
            indices[i] += 1
            for j in range(i + 1, r):
                indices[j] = indices[j - 1] + 1
            yield list(pool[i] for i in indices)

list(powerset([1, 2, 3, 4]))