python generator yield 协程 coroutine

参考

生成器

协程

提高：现在还是看不懂

Python “黑魔法” 之 Generator Coroutines

代码分析

#!/usr/bin/env python

import time

def consumer():
r = ''
while True:
n = yield r
print '[CONSUMER] Consuming ', n
time.sleep(1)
r = '200 OK'

def produce(c):
print 'c.next:', c.next()
n = 0
while n < 5:
n += 1
print '[PRODUCER] Producing ', n
r = c.send(n)
print '[PRODUCER] Consumer return: ', r
c.close()

if __name__ == '__main__':
c = consumer()
produce(c)

输出：

c.next:
[PRODUCER] Producing  1
[CONSUMER] Consuming  1
[PRODUCER] Consumer return:  200 OK
[PRODUCER] Producing  2
[CONSUMER] Consuming  2
[PRODUCER] Consumer return:  200 OK
[PRODUCER] Producing  3
[CONSUMER] Consuming  3
[PRODUCER] Consumer return:  200 OK
[PRODUCER] Producing  4
[CONSUMER] Consuming  4
[PRODUCER] Consumer return:  200 OK
[PRODUCER] Producing  5
[CONSUMER] Consuming  5
[PRODUCER] Consumer return:  200 OK

从main开始，首先是生成器实例化

c = consumer()

然后把这个生成器作为参数扔到produce函数里。

c.next()

先执行第一遍的consumer。一直到遇上yield，yield把r返回给调用者。但是对consumer而言，只是将r返回了，n还没接收到东西（没接收到produce的send）

r = ''
while True:
n = yield r

在这里，其实给c.next()返回了一个空字符串r，produce函数接收到空字符串后将其输出。

在produce函数继续执行，输出

[PRODUCER] Producing  1

然后给cosumer发送了n=1

r = c.send(n)

consumer获得了1

n = yield r

将其输出

[CONSUMER] Consuming  1

然后consumer休眠1秒，然后将r赋值，再循环，执行到yield，给produce函数返回了

r = '200 OK'

produce函数接收到回复r，将r打印出来

[PRODUCER] Consumer return:  200 OK

如此循环下去。