python函数高级特性之生成器

**将列表中的所有字符串转换为小写：

li = ["Hello", "WESTOS", 1, 43]

[i. lower() for i in li if isinstance(i,str)]

 

案例1：[i for i in range(10000000)]

如上，用列表生成式打印一串数字，当生成时元素即打印，会占用内存，range后面的数越大，越占内存。为了解决这一问题，可以引用生成器：

(i for i in range(10000000))  ##注意此处用的是小括号

读取生成器元素的方式：

法一：g.next()                ##一次返回一个值，当next次数大于生成个数时会报错

法二：from collections import Iterable

          g = (i**2 for i in range(4))

          print isinstance(g.Iterable)

          for i in g:

          print i             ##此处利用生成器的可迭代性

 

案例2：Fibonacci数列：[1, 1, 2, 3, 5, 8, 13, 21,...]

*生成fib数列的函数，n代表生成数个数

def fib(n):

n, a, b = 0, 0, 1

while n < max:

print b

a, b = b, a + b

n += 1

fib(10)

使用yield关键字（输出生成器）生成Fibonacci数列：

def fib(n):

n, a, b = 0, 0, 1

while n < max:

yeild b

a, b = b, a + b             

n += 1

g = fib(10)

for i in g:

print i

**python中两值交换：x, y = y, x

 

案例3：生成器生成生产者消费者模型

coding:utf-8

latiao_agency = []

kind = ["丢丢辣", "微辣", "麻辣", "特辣", "超级辣"]

 

def consumer(name):

print "%s 准备买辣条" %(name)

while True:

kind = yield

latiao_agency.remove(kind)

print "客户[%s]买了[%s]口味的辣条。。。。。。" %(name,kind)

 

    #g = consumer("肃敏")

    #g.next()

    ##send方法将值传给yield所在位置的变量；

    #g.send("特辣")

 

    import time

    def producer(name, *kind):

        #c1和c2是生成器对象

        #c1 = consumer("肃敏")

        #c2 = consumer("小闫")

        #c1.next()

        #c2.next()

 

     print "准备制作辣条。。。。。。"

     for i in kind:

         time.sleep(3)

         print "[%s]制作了[%s]口味的辣条，准备提供给消费者。。。。。。" %(name, i)

         latiao_agency.append(i)

         #c1.send(i)

         #c2.send(i)

 

producer("长虹", "微辣", "麻辣", "超级辣")

c1 = consumer("肃敏")

c1.next()

c1.send("微辣")

print "目前本店辣条口味："

for i in latiao_agency:

print i

 

案例4：迷你聊天机器人

#coding:utf-8

#函数中有yield，代表调用函数时，返回值为生成器；

def chat_robot():

        res = ''

        while True:

         #遇到yield时停止运行

            received = yield res

            if '你好' in received or 'hi' in received:

                res = "你好，欢迎来到火星！我是小伊！"

            elif '多少岁' in received or 'age' in received:

                res = "我永远8岁！"

            elif '再见' in received or 'bye' in received:

                res = "再见！"

            else:

                res = "我不知道你在说什么，请说人话！"

 

#Chat是生成器

Chat = chat_robot()

    #Chat.next()和next(Chat)效果相同；

    next(Chat)

 

    while True:

        r_input = raw_input("我>>")

        if not r_input:

            continue

        elif r_input.lower() == 'q':

            print "已退出！"

            break

        else:

            response = Chat.send(r_input)

            print response