迭代器协议

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

# l=list(‘hello‘)
# for i in l:
#     print(i)
f1=Foo(10)
print(f1.__next__())        #11
print(f1.__next__())        #12
print(f1.__next__())        #13
print(f1.__next__())        #StopIteration: 终止了

# for i in f1:      # obj=iter(f1)------------>f1.__iter__()
#      print(i)     #obj.__next_()

class Fib:
    def __init__(self):
        self._a=1
        self._b=1

    def __iter__(self):
        return self

    def __next__(self):
        if self._a>100:
            raise StopIteration(‘终止‘)
        self._a,self._b=self._b,self._a+self._b
        return self._a

f1=Fib()
print(next(f1))
print(next(f1))
print(next(f1))
print(next(f1))
print(next(f1))
print(‘==============‘)
for i in f1:
    print(i)
    
# 1
# 2
# 3
# 5
# 8
# ==============
# 13
# 21
# 34
# 55
# 89
# 144