生成器（generator），迭代器（yield）

g=(i for i in range(10)) #小括号表示生成一个迭代生成器。[]是列表生成器
g.__next__()

yield将一个函数变成生成器

import time
def f():
    for i in range(10):
        yield i  #如果换成return i，则最终只能返回0。
        print('aa')
m=f()    #m是一个generator
print(m)
print(dir(m))
print(m.__next__())
print(m.__next__())
time.sleep(2)
print(m.__next__())

 按字节读取文本：

def rb():
    f=open('e:\a.txt','rb')
    while True:
        size=6 #每次读取6个字节
        block=f.read(size)
        if block:
            yield block
        else:
            break
    f.close()
rr=rb()
for r in rr:
    print r

yield中的next()和send()：

def yed():
    print "enter fun",
    yield 10
yy = yed()
yy.next() #返回"enter fun"
print yy.next() #返回 enter fun 10



def yed():
    print "enter fun",
    yield 10
    print "next1"
    yield 20
yy = yed()
yy.next()
yy.next()
# #返回enter fun next1


def yed():
    print "enter fun",
    yield 10
    print "next1"
    yield 20
yy = yed()
yy.next()
yy.send('hello') #此处send的参数hello被yield 10接收了，但是并没有进行打印，所以不会被打印
#返回enter fun next1



def yed():
    print "enter fun",
    y1 = yield 10
    print "next1",
    print y1
    yield 20
yy = yed()
yy.next()
yy.send('hello') #send发送的值会成为当前yield的结果，即yield 10，即y1，并且send的返回结果是下一个yield的结果（相当于了next()）
#返回 enter fun next1 hello



def yed():
    print "enter fun",
    y1 = yield 10
    print "next1",
    print y1
    y2 = yield 20

yy = yed()
mn = yy.next() #结果为yield 10的参数，即10
ms = yy.send('hello') #结果为yield 20的参数，即20。hello被y1接收到了

print 'mn: %s, ms: %s' %(mn,ms)
#返回enter fun next1 hello
#mn: 10, ms: 20

　　第一次调用时，要使用next()语句或是send(None)，不能使用send发送一个非None的值，否则会出错的，因为没有yield语句来接收这个值。所以第一次时next() == send(None)
send(msg) 和 next()是有返回值的，它们的返回值很特殊，返回的是下一个yield表达式的参数。比如yield 10，则返回10 。

协同处理数据：http://www.tuicool.com/articles/VBfAzaQ

　　我们现在利用yield关键字会自动冻结函数堆栈的特性，想象一下，假如现在有两个函数f1()和f2(),各自包含yield语句，见下例。主线程先启动f1(), 当f1()执行到yield的时候，暂时返回。这时主线程可以将执行权交给f2()，执行到f2()的yield后，可以再将执行权交给f1()，从而实现了在同一线程中交错执行f1()和f2()。f1()与f2()就是协同执行的程序，故名协程。

import random

#消费生成的数据
def consume():
    print 'waiting to consume'
    while True:
        data = yield
        sum_data = sum(data)
        print '%s was consumed,the sum is %d ' %(str(data),sum_data)

#生成数据
def produce():
    print 'begin to produce'
    consumer = consume()
    consumer.next()
    while True:
        data = random.sample(range(10),3)
        print '%s produced' %(str(data))
        consumer.send(data)
        yield


producer = produce()
for i in range(5):
    producer.next()    #直接执行produce()里面的代码：在produce里面先生成data，然后再将其发送给consume

可以优化为如下：

import random

#消费生成的数据
def consume():
    print 'waiting to consume'
    while True:
        data = yield
        sum_data = sum(data)
        print '%s was consumed,the sum is %d ' %(str(data),sum_data)

#生成数据
def produce(consumer):
    print 'begin to produce'
    while True:
        data = random.sample(range(10),3)
        print '%s produced' %(str(data))
        consumer.send(data)
        yield


consumer = consume()
producer = produce(consumer)
consumer.next() #打印waiting to consum


for i in range(5):
    producer.next()    #直接执行produce()里面的代码：在produce里面先生成data，然后再将其发送给consume

返回结果如下：

waiting to consume
begin to produce
[2, 9, 3] produced
[2, 9, 3] was consumed,the sum is 14 
[1, 5, 2] produced
[1, 5, 2] was consumed,the sum is 8 
[8, 5, 4] produced
[8, 5, 4] was consumed,the sum is 17 
[6, 1, 2] produced
[6, 1, 2] was consumed,the sum is 9 
[8, 6, 3] produced
[8, 6, 3] was consumed,the sum is 17 

异步并发？？？？

from time import sleep,ctime

def consumer(name):
    print '%s want to consume' % name
    while True:
        bb = yield
        print '%s was consumed by %s' %(bb,name)

def producer(pname):
    c1=consumer('A')
    c2=consumer('B')
    c1.next()
    c2.next()
    print '%s begin to produce' % pname

    for i in range(5):
        sleep(1)
        print '%s produce 2' % pname
        c1.send(i)
        c2.send(i)

producer('zhangsan')

返回结果如下：

A want to consume
B want to consume
zhangsan begin to produce
zhangsan produce 2
0 was consumed by A
0 was consumed by B
zhangsan produce 2
1 was consumed by A
1 was consumed by B
zhangsan produce 2
2 was consumed by A
2 was consumed by B
zhangsan produce 2
3 was consumed by A
3 was consumed by B
zhangsan produce 2
4 was consumed by A
4 was consumed by B

继续看这个-2016.5.3  http://my.oschina.net/u/877348/blog/184058