协程

协程是线程中更小的单位：

　　一、可以通过greenlet实现协程的调度

　　

from greenlet import greenlet

def test1():
    print ("12")
    t2.switch()
    print ("34")
    t2.switch()
def test2():
    print ("56")
    t1.switch()
    print ("78")
if __name__=="__main__":
    t1 = greenlet(test1) #启动协程
    t2 = greenlet(test2) #启动协程
    t1.switch()

二、gevent 是一个第三方库，可以轻松通过gevent实现并发同步或异步编程，在gevent中主要用到的是greenlet，它是以c扩展模块模式接入python的
轻量协程，greenlet全部运行在主程序操作的内部，但它们被协程式调用(greenlet是手动切换、gevent是自动切换）。

import gevent

def bar1():
    print ("The bar is begin!")
    gevent.sleep(3)
    print("The bar is end!")

def bar2():
     print ("The bar2 is begin!")
     gevent.sleep(2)
     print ("The bar2 is end!")
def bar3():
    print ("The bar3 is begin!")
    gevent.sleep(1)
    print ("The bar3 is end!")

gevent.joinall([
    gevent.spawn(bar1),
    gevent.spawn(bar2),
    gevent.spawn(bar3)
])

三、协程实现简单的爬虫操作；

from urllib import request
import time,gevent
from gevent import monkey
monkey.patch_all() #把当前的所有io操作打上标记；

def f(url):
    print("Get:%s",url)
    resp = request.urlopen(url)
    data = resp.read()
    print("%d bytes receive from %s." % (len(data),url))

urls = [
    "https://www.python.org/",
    "https://www.yahoo.com/",
    "https://www.github.com/"
]
time_start = time.time()
for url in urls: #同步串行；
    f(url)
print ("同步cost:",time.time() - time_start)

async_time_start = time.time()
gevent.joinall([ #异常并行；
    gevent.spawn(f,"https://www.python.org/"),
    gevent.spawn(f,"https://www.yahoo.com/"),
    gevent.spawn(f,"https://www.github.com/"),
])
print ("异步cost:",time.time() - async_time_start)

转载于:https://www.cnblogs.com/wulafuer/p/7965500.html