总结协程特点：
 
必须在只有一个单线程里实现并发
修改共享数据不需加锁
用户程序里自己保存多个控制流的上下文栈
附加：一个协程遇到IO操作自动切换到其它协程（如何实现检测IO，yield、greenlet都无法实现，就用到了gevent模块（select机制））
 
同步和异步的速度对比
 
 
 
from urllib import request
import gevent,time
from gevent import monkey

monkey.patch_all()#把当前程序的所以的io操作，做上标记


def get(url):#下载网页信息
    print(" getting %s" % url)
    response = request.urlopen(url)
    data = response.read()
    print("%s is parse,parse result:%s" % (url, len(data)))

urls = [
        "https://www.taobao.com/",
        "https://www.jd.com/",
        "https://www.python.org/",
        "https://www.baidu.com/",
        "https://www.openstack.org/"
    ]
times = time.time()
for url in urls:
    get(url)
print("同步%s" % (time.time()-times))


async_starttime = time.time()
gevent.joinall([gevent.spawn(get,"https://www.taobao.com/"),
                gevent.spawn(get,"https://www.jd.com/"),
                gevent.spawn(get,"https://www.python.org/"),
                gevent.spawn(get,"https://www.baidu.com/"),
                gevent.spawn(get,"https://www.openstack.org/")])
print("异步%s" % (time.time()-async_starttime))
 
结果：
 
 getting https://www.taobao.com/
https://www.taobao.com/ is parse,parse result:151199
 getting https://www.jd.com/
https://www.jd.com/ is parse,parse result:109776
 getting https://www.python.org/
https://www.python.org/ is parse,parse result:48821
 getting https://www.baidu.com/
https://www.baidu.com/ is parse,parse result:227
 getting https://www.openstack.org/
https://www.openstack.org/ is parse,parse result:65075
同步3.7612645626068115
 getting https://www.taobao.com/
 getting https://www.jd.com/
 getting https://www.python.org/
 getting https://www.baidu.com/
 getting https://www.openstack.org/
https://www.taobao.com/ is parse,parse result:151199
https://www.baidu.com/ is parse,parse result:227
https://www.jd.com/ is parse,parse result:109776
https://www.openstack.org/ is parse,parse result:65075
https://www.python.org/ is parse,parse result:48821
异步1.4034960269927979

Process finished with exit code 0
 
异步比同步快2.3秒，提升明显