Python笔记（十八）：协程asyncio

（一）asyncio

1、asyncio 用async 修饰词来声明异步函数

2、asyncio.create_task(异步函数)来创建任务

3、通过await asyncio.gather(任务)来执行任务

4、通过asyncio.run(函数)来触发运行

5、一个比较好的方式是asyncio.run(main())作为程序入口，在程序运行周期内，只调用一次asyncio.run()

例如：请求5次这个url https://www.java.com/zh_CN/

用协程是3.8s,不用协程9.2s。当然这个时间对比可能不是非常准确，因为请求过程还受其他因素影响，不过应该能大致说明问题。

代码语言：javascript复制

 1 import datetime
 2 
 3 import asyncio
 4 import aiohttp
 5 
 6 header = {
 7     "User-Agent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36",
 8     "Host":"c.oracleinfinity.io",
 9     "Accept-Encoding":"gzip, deflate, br",
10     "accept":"text/html,application/xhtml xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9"
11 }
12 async def fetch_content(url):
13     async with aiohttp.ClientSession(
14         headers=header,connector=aiohttp.TCPConnector(ssl=False)
15     ) as session:
16         async with session.get(url) as response:
17             return await response.text()
18 
19 async def main():
20     url = "https://www.java.com/zh_CN/"
21     urls = [url for i in range(5)]
22     tasks = [asyncio.create_task(fetch_content(url)) for url in urls]
23     pages = await asyncio.gather(*tasks)  #*表示解包列表，解包字典则用2个星号**
24 
25 
26 start_time = datetime.datetime.now()
27 print(start_time)
28 asyncio.run(main())
29 end_time = datetime.datetime.now()
30 print(end_time - start_time)

不用协程

代码语言：javascript复制

import requests
import datetime

header = {
    "User-Agent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36",
    "Host":"c.oracleinfinity.io",
    "Accept-Encoding":"gzip, deflate, br",
    "accept":"text/html,application/xhtml xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9"
}

def main():
    url = "https://www.java.com/zh_CN/"
    for i in range(5):
        page = requests.get(url,headers=header).content


start_time = datetime.datetime.now()
print(start_time)
main()
end_time = datetime.datetime.now()
print(end_time - start_time)