python coroutine

前言

OOAD课程是用python教的，其中涉及到大量的python语法糖，老师也算是手把手教如何写出OO的python，但一个学期没听课只能期末补一补。

Coroutines

Coroutines are similar to generators with a few differences. The main differences are:

generators are data producers generators制造数据

coroutines are data consumers coroutines消费数据

来看第一个代码示例，通过send()接收数据，然后进行比对，找出含有关键字的数据并打印。

def grep(pattern):

print("Searching for", pattern)

while True:

line = (yield)

if pattern in line:

print(line)

search = grep('coroutine')

next(search)

# Output: Searching for coroutine

search.send("I love you")

search.send("Don't you love me?")

search.send("I love coroutines instead!")

很明显我们可以看到，yield关键字在这里已经从返回数据的变为接收数据的。也就是，Python的yield不但可以返回一个值，它还可以接收调用者发出的参数。

在中文里，coroutine对应的是协程，但是显然老师的重点不是什么同步异步，而是yield，以及coroutine和subprogram的区别。

Subprogram vs Coroutine, is (programming) a piece of code that performs a task, and that can be passed new input and return output more than once. As nouns the difference between subroutine and coroutine is that subroutine is (computer science) a section of code, called by the main body of a program, that implements a task while coroutine is (programming) a piece of code that performs a task, and that can be passed new input and return output more than once.

放上老师PPT的测试代码就收工：

def coroutine(y):

for i in range(y):

x = yield i

print("i=%d , x=%d " % (i, x))

c = coroutine(4)

next(c)

c.send(10)

c.send(20)

c.send(30)

def echo():

just_received='nothing'

try:

while True:

received=yield just_received

just_received=received

print('I got {}.'.format(just_received))

except GeneratorExit:

# when closed with close()

print('Coroutine closed!')

g = echo()

next(g)

g.send('test1')

g.send('test2')

g.close()

Reference