python生成器的调用理解

import sys

def fibonacci(n): # 生成器函数 - 斐波那契

    a, b, counter = 0, 1, 0

    while True:

        if (counter > n):

            return

        yield a

        a, b = b, a + b

        counter += 1

f = fibonacci(10) # f 是一个迭代器，由生成器返回生成

while True:

    try:

        print (next(f), end=" ")

    except StopIteration:

        sys.exit()