• 使用迭代器反转

a = [1, 2, 3, 4]for x in reversed(a):    print(x)class Countdown:    def __init__(self, start):        self.start = start    def __iter__(self):        n = self.start        while n > 0:            yield n            n -= 1    def __reversed__(self):        n = 1        while n <= self.start:            yield n            n += 1for i in reversed(Countdown(5)):    print(i)for i in Countdown(5):    print(i)

out

43211234554321