# -*- coding: utf-8 -*-

"""

Created on Fri Mar 16 15:24:29 2018

@author: User

"""

#yield 使用浅析

#method1

def fab(max):

n, a, b = 0, 0, 1

while n < max:

print(b)

a, b = b, a + b

n = n + 1

fab(5)

#method2: 耗用内存大

def fab(max):

n, a, b = 0, 0, 1

L = []

while n < max:

L.append(b)

a, b = b, a + b

n = n + 1

return L

#method3

class Fab(object):

def __init__(self, max):

self.max = max

self.n, self.a, self.b = 0, 0, 1

def __iter__(self):

return self

def next(self):

if self.n < self.max:

r = self.b

self.a, self.b = self.b, self.a + self.b

self.n = self.n + 1

return r

raise StopIteration()

for n in Fab(5):

print(n)

#method4

def fab(max):

n, a, b = 0, 0, 1

while n < max:

yield b

# print b

a, b = b, a + b

n = n + 1

for n in fab(5):

print(n)

'''

yield 的作用就是把一个函数变成一个 generator，带有 yield 的函数不再是一个普通函数，

Python 解释器会将其视为一个generator，调用fab(5)不会执行fab函数，而是返回一个iterable对象

yield必须在function里面使用，不能直接用在function外面

'''