自从python2.2提供了yield关键字之后，python的生成器的很大一部分用途就是可以用来构建协同程序，能够将函数挂起返回中间值并能从上次离开的地方继续执行。python2.5的时候，这种生成器更加接近完全的协程，因为提供了将值和异常传递回到一个继续执行的函数中，当等待生成器的时候，生成器能返回控制。
python提供的生成器设施：
python封装
虽然python3提供了asyncio这样的异步IO库，而且也有greenlet等其他协程库，但目前的需求并不是实际的网络IO并发操作，而是需要模拟状态机的运行，因此使用协程可以很方便的模拟，并加入认为的控制，下面是封装的一个python类。
class Coroutine(object):
""" Base class of the general coroutine object """
STATE_RUNNING = 0
STATE_WAITING = 1
STATE_CLOSING = 2
def __init__(self):
self.state = Coroutine.STATE_WAITING
self.started = False
self.args = None
self.routine = self._co()
def _co(self):
self.ret = None
while True:
self.args = yield self.ret
if not self.started:
self.started = True
continue
else:
self.state = Coroutine.STATE_RUNNING
self.ret = self.run(self.args)
if self.state == Coroutine.STATE_CLOSING:
break
self.state = Coroutine.STATE_WAITING
def start(self):
""" Start the generator """
if self.routine is None:
raise RuntimeError('NO task to start running!')
self.started = True
self.routine.next()
def finish(self):
""" Finish the execution of this routine """
self.state = Coroutine.STATE_CLOSING
self.routine.close()
def run(self, args):
""" The runing method to be executed every once time"""
raise NotImplementedError
def execute(self, arg_obj):
""" Awake this routine to execute once time """
return self.routine.send(arg_obj)
基于上述封装，下面实现了一个协同的生产者消费者示例：
class ProducerCoroutine(Coroutine):
""" The Producer concrete coroutine """
def __init__(self, cnsmr):
if not isinstance(cnsmr, Coroutine):
raise RuntimeError('Consumer is not a Coroutine object')
self.consumer = cnsmr
self.consumer.start()
super(ProducerCoroutine, self).__init__()
def run(self, args):
print 'produce ', args
ret = self.consumer.execute(args)
print 'consumer return:', ret
def __call__(self, args):
""" Custom method for the specific logic """
self.start()
while len(args) > 0:
p = args.pop()
self.execute(p)
self.finish()
class ConsumerCoroutine(Coroutine):
""" The Consumer concrete coroutine """
def __init__(self):
super(ConsumerCoroutine, self).__init__()
def run(self, args):
print 'consumer get args: ', args
return 'hahaha' + repr(args)
运行结果如下：
produce 4 consumer get args: 4 consumer return: hahaha4 produce 3 consumer get args: 3 consumer return: hahaha3 produce 2 consumer get args: 2 consumer return: hahaha2 produce 1 consumer get args: 1 consumer return: hahaha1 produce 0 consumer get args: 0 consumer return: hahaha0
