可以直接作用於for迴圈的物件統稱為可迭代物件：Iterable

可以被next()函式呼叫並不斷返回下一個值的物件稱為迭代器：Iterator

參考：Python學習筆記 - 迭代器Iterator

用迭代器實現斐波那契數列

Python3環境下可實現迭代：

class Fib(object):
    def __init__(self, max):
        super(Fib, self).__init__()
        self.max = max

    def __iter__(self):
        self.a = 0
        self.
 
b = 1
        return self

    def __next__(self):
        fib = self.a
        if fib > self.max:
            raise StopIteration
        self.a, self.b = self.b, self.a + self.b
        return fib

# 定義一個main函式，迴圈遍歷每一個菲波那切數
def main():
    # 20以內的數
    fib = Fib(20)
    for i in fib:
        print
 
(i)

# 測試
if __name__ == '__main__':
    main()

0
1
1
2
3
5
8
13

Python2環境下執行報錯：

TypeError: iter() returned non-iterator of type ‘Fib’

def _next_(self) is for Python 3

For Python 2 you need to add method next()

class Fib(object):
    def __init__(self, max):
        super(Fib, self).__init__(
 
)
        self.max = max

    def __iter__(self):
        self.a = 0
        self.b = 1
        return self

    def __next__(self):
        fib = self.a
        if fib > self.max:
            raise StopIteration
        self.a, self.b = self.b, self.a + self.b
        return fib

    def next(self):
        return self.__next__()


def main():
    fib = Fib(20)
    for i in fib:
        print(i)

if __name__ == '__main__':
    main()