__iter__和__next__

目录

• __iter__(self)和__next__(self)

__iter__(self)和__next__(self)

Python中for循环的原理就是调用可迭代对象的__iter__方法得到迭代器对象，然后调用__next__方法进行取值，直到对象抛出StopIteration异常。某些语言例如go，即支持迭代循环，也支持索引循环。

自定义一个可迭代对象模拟range：

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:
            n = self.start
            self.start += self.step
            return n
        raise StopIteration()

for i in Range(0,100,):
    print(i)

产生小于num的斐波那契数列：

class Fib:
    def __init__(self, n):
        self.n = n
        self.start = 0
        self.second = 1

    def __iter__(self):
        return self

    def __next__(self):
        if self.start < self.n:
            x = self.start
            self.start, self.second = self.second, self.start + self.second
            return x
        raise StopIteration()


for i in Fib(100):
    print(i, end=' ')

0 1 1 2 3 5 8 13 21 34 55 89

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