必须写 if not flag: 吗？不写也能运行啊

s1 = set([1, 2, 3, 4, 6, 8, 10])

s2 = set([1, 2, 3, 4, 5, 6, 7, 8, 9])

flag = s1.isdisjoint(s2)

for item in s1:

    if item not in s2:

        continue

    print(item)