协程及其原理和应用

1.协程

import gevent


def foo():
    print('Running in foo')
    gevent.sleep(0)
    print('Explicit context switch to foo again')


def bar():
    print('Explicit context to bar')
    gevent.sleep(0)
    print('Implicit context switch back to bar')
'''
遇到sleep就切换到下一个
'''

gevent.joinall([
    gevent.spawn(foo),
    gevent.spawn(bar),
])

结果显示：如注释所写，遇到sleep就切换。

Running in foo
Explicit context to bar
Explicit context switch to foo again
Implicit context switch back to bar

2.协程原理

def consumer(name):
    print("--->starting eating baozi...")
    while True:
        new_baozi = yield
        print("[%s] is eating baozi %s" % (name, new_baozi))
        # time.sleep(1)


def producer():
    r = con.__next__()
    r = con2.__next__()
    n = 0
    while n < 5:
        n += 1
        con.send(n)
        con2.send(n)
        print("33[32;1m[producer]33[0m is making baozi %s" % n)


if __name__ == '__main__':
    con = consumer("c1")
    con2 = consumer("c2")
    p = producer()

上述的代码是之前所学到的吃包子。其中几点注意：

1.只有含有yield的函数才能有next方法。现在一般为next（conn）

2.执行next方法后函数才会运行（函数加括号不能启动函数），遇到yield后冻结，返回yield后的值给调用next的对象。

3.send也有next的效果，但是是将自己值送给yield前面的变量。但是不能先手send。send不能启动函数

结果显示：

--->starting eating baozi...
--->starting eating baozi...
[c1] is eating baozi 1
[c2] is eating baozi 1
[producer] is making baozi 1
[c1] is eating baozi 2
[c2] is eating baozi 2
[producer] is making baozi 2
[c1] is eating baozi 3
[c2] is eating baozi 3
[producer] is making baozi 3
[c1] is eating baozi 4
[c2] is eating baozi 4
[producer] is making baozi 4
[c1] is eating baozi 5
[c2] is eating baozi 5
[producer] is making baozi 5

3.爬虫

from gevent import monkey
import time

monkey.patch_all()   # 监听IO口的程序 大量节约时间
import gevent
from  urllib.request import urlopen


def f(url):
    print('GET: %s' % url)
    resp = urlopen(url)
    data = resp.read()
    print('%d bytes received from %s.' % (len(data), url))
start = time.time()

gevent.joinall([
    gevent.spawn(f, 'https://www.python.org/'),
    gevent.spawn(f, 'https://www.yahoo.com/'),
    gevent.spawn(f, 'https://github.com/'),
])

print(time.time()-start)

只是简单讲主页的数据全爬了一遍没做处理。