next和iter可迭代协议

python中，对象中实现了__iter__方法就是可迭代对象
实现了__next__方法就是迭代器

代码示例

from collections import Iterator,Iterable

class Foo:

    def __next__(self):
        pass

    def __iter__(self):
        pass

f= Foo()
print(isinstance(f,Iterator))
print(isinstance(f,Iterable))

执行结果

True
True

实现一个斐波那契数列

代码：

class Fib:
    def __init__(self):
        self._a=0
        self._b=1

    def __iter__(self):
        return self

    def __next__(self):
        self._a, self._b = self._b, self._a + self._b
        return self._a

f = Fib()
print(next(f))
print(next(f))
print(next(f))
print(next(f))

执行结果

1
1
2
3

模拟range函数

class RANGE:
    def __init__(self,start,stop,step=1):
        self.start = start
        self.stop = stop
        self.step = step

    def __iter__(self):
        return self
    def __next__(self):
        if self.start >= self.stop:
            raise StopIteration
        res = self.start
        self.start +=self.step
        return res

for i in RANGE(2,10,2):
    print(i)

执行结果

2
4
6
8