迭代器协议

l = list("hello")         #这就是在做实例化，list是一个类
for i in l:               #先将一个对象执行__iter__()
    print(i)

#迭代器协议：通过__iter__将一个对象变成可迭代对象，再调用__next__()方法进行迭代下一项
class Foo:
    def __init__(self,n):
        self.n = n

    def __iter__(self):
        return self

    def __next__(self):
        if self.n == 13:
            raise StopIteration("终止了")
        self.n += 1
        return self.n

f1 = Foo(10)
# print(f1.__next__())
# print(f1.__next__())
# print(f1.__next__())
# print(f1.__next__())

for x in f1:print(x)         #for循环会抓捕到结束的异常，然后终止


#斐波那契数列：下一个值是上两个值的和。如1,2,3,5,8
class Fib:
    def __init__(self,m,n):
        self.m = m
        self.n = n

    def __iter__(self):
        return self
    def __next__(self):
        if self.m > 100:
            raise StopIteration("终止")
        self.m,self.n = self.n,self.m+self.n
        return self.m

fb1 = Fib(1,2)
print(fb1.__next__())
for z in fb1:print(z)