协程

socket发送请求:两种方式

方式一:

import socket
import requests
key_list=['alex','db','sb']

for item in key_list:
    ret = requests.get('https://www.baidu.com/s?wd=%s' %item)

方式二:

import socket

def get_data(key):

    client=socket.socket()
    client.connect(('www.baidu.com',80))
                
    client.sendall(b'GET /s?wd=%s HTTP/1.0
host:www.baidu.com

'%key)

    chuck_list=[]
    while True:
        chuck=client.recv(1024)
        if not chuck:
            break
        chuck_list.append(chuck)
    body=b''.join(chuck_list)
    print(body.decode(utf-8))

key_list=['alex','db','sb']
for item in key_list:
    get_data(item)

解决线程阻塞:

import socket
client=socket.socket()
client.setblocking(False)

try:
    client.connect(('www.baidu.com',80))
except BlockingIOError as e:
    pass
client.sendall(b'GET /s?wd=alex HTTP/1.0
host:www.baidu.com

')

chuck_list=[]
while True:
       chuck=client.recv(1024)

       if not chuck:
           break
       chuck_list.append(chuck)

body=b''.join(chuck_list)
print(body.decode(utf8))

单线程的并发:

        wimport socket
import select

client1=socket.socket()
client1.setblocking(False)
try:
    client1.connect((www.baidu.com',80))
except BlockingIOError as e:                
        pass

client2=socket.socket()
client2.setblocking(False)
try:
    client2.connect((www.sogou.com',80))
except BlockingIOError as e:                
        pass

client3=socket.socket()
client3.setblocking(False)
try:
    client3.connect((www.oldbouedu.com',80))
except BlockingIOError as e:                
        pass

socket_list=[client1,client2,client3]
conn_list=[client1,client2,client3]
while True:
     rlist,wlist,elist=select.select(socket_list,conn_list,[],0.005)
     for sk in wlist:
         if sk ==client1:
            sk.sendall(b'GET /S?wd=alex HTTP/1.0
host:www.baidu.com

)
        if sk ==client2:
            sk.sendall(b'GET /web?query=fdf HTTP/1.0
host:www.sogou.com

)    
        if sk ==client3:
            sk.sendall(b'GET /S?wd=alex HTTP/1.0
host:www.oldboyedu.com

)

for sk in rlist:
    chuck_list=[]
    while True:
            try:
                chuck=sk.recv(1024)
                if not chuck:
                     break
                chuck_list.append(chuck)
            except BlockingIOError as e:
                break
    body = b''.join(chuck_list)
    print('------>',body)
    sk.close()
    socket_list.remove(sk)
if not socket_list:
    break

IO多路复用:

检测多个socket是否发生变化.是否连接成功,是否收到数据.

操作系统检测socket是否发生变化有三种方法:select :最多检测1024个socket,循环去检测  pool:不限制监听的个数,循环去检测(水平触发).  epool:不限制监听socket个数,回调方式,(边缘触发).

异步非阻塞:

提高并发的方案:三种

---多线程

---多进程

---异步非阻塞模块(Twisted)   scrapy框架(单线程完成并发

非阻塞:创建多个客户端,对服务端进行访问,在connect,和recv操作时都会发生阻塞现象,设置setblocking(False),在执行以上操作时就不需要等待,直接发送过以后就执行下一个客户端的连接请求,以此类推.但是最后会报BlockingIOError错误,用try,except捕获一下就ok

异步: 执行完之后会自动执行回调函数或者自动执行某些操作,比如爬虫中向某个网站发送请求,执行完成以后执行回调函数

协程IO切换:greenlet   gevent

import greenlet

def f1():
    print(11) 
    gr2.swith()
    print(22)
    gr2.swith()

def f2():
    print(33)
    gr1.switch()
    print(44)

gr1=greenlet.greenlet(f1)
gr2=greenlet.greenlet(f2)
gr1.switch()

打印结果为:
11 33  22  44

from gevent import monkey
monkey.patch_all()
import requests
import gevent

def get_page1(url1):
    ret = requests.get(url1)
    print(url,ret.content)

def get_page2(url1):
    ret = requests.get(url1)
    print(url,ret.content)

def get_page3(url1):
    ret = requests.get(url1)
    print(url,ret.content)

gevent.joinall([
    gevent.spawn(get_page1, 'https://www.python.org/'), # 协程1
    gevent.spawn(get_page2, 'https://www.yahoo.com/'),  # 协程2
    gevent.spawn(get_page3, 'https://github.com/'),     # 协程3
])

基于yield实现协程:

def f1():
    print(11)
    yield
    print(22)
    yield
    print(33)

def f2():
    print(55)
    yield
    print(66)
    yield
    print(77)

v1 = f1()
v2 = f2()

next(v1) # v1.send(None)
next(v2) # v1.send(None)
next(v1) # v1.send(None)
next(v2) # v1.send(None)
next(v1) # v1.send(None)
next(v2) # v1.send(None)