class Countlist:
    def __init__(self,*args):
        self.values = [x for x in args]
        self.count={}.fromkeys(range(len(self.values)),0)
    def __len__(self):
        return len(self.values)
    def __getitem__(self, key):
        self.count[key]+=1
        return self.values[key]

class Fibs:
    def __init__(self):
        self.a=0
        self.b=1
    def __iter__(self):
        return self
    def __next__(self):#这里改写了next方法
        self.a,self.b=self.b,self.a+self.b
        return  self.a

fibs=Fibs()
for each in fibs:
    if each <1000:
        print(each)
    else:
        break
        

class Fibs:
    def __init__(self,n=20):
        self.a=0
        self.b=1
        self.n=n
    def __iter__(self):
        return self
    def __next__(self):
        self.a,self.b=self.b,self.a+self.b
        if self.a>self.n:
            raise  StopIteration
        return  self.a

fibs=Fibs(1000)
for each in fibs:
    print(each)

结果

D:\recent\code\venv\Scripts\python.exe D:/recent/code/venv/test.py
1
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987

下面用生成器也可以

def fibs():
    a=0
    b=1
    while True:
        a,b=b,a+b
        yield a


for each in fibs():
    if each>1000:
        break
    print(each)

结果

D:\recent\code\venv\Scripts\python.exe D:/recent/code/venv/test.py
1
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987