python——异步编程代码实战

摘要

主要介绍python中相关的异步编程的原理和是代码的实战

协程实现

协程(Coroutine)，也可以被称为微线程，是一种用户态内的上下文切换技术。简而言之，其实就是通过一个线程实现代码块相互切换执行。协程不是计算机提供，程序员人为创造。

协程的优点：在一个线程中如果遇到IO等待时间，线程不会傻傻等，利用空闲的时候再去干点其他事。

greenlet 实现协程

from greenlet import greenlet

def fun1():
    print(1)
    gr2.switch()
    print(2)
    gr2.switch()

def fun2():
    print(3)
    gr1.switch()
    print(4)

gr1 = greenlet(fun1)
gr2 = greenlet(fun2)

gr1.switch()

yield 关键字（在企业的代码不会使用）

def fun3():
    yield 1
    yield from fun4()
    yield 2

def fun4():
    yield 3
    yield 4

f = fun3()
for item in f:
    print(item)

#显示的结果
----------------------------------------------------
1
3
4
2

asyncio 装饰器（py3.4）

import asyncio

@asyncio.coroutines
def fun5():
    print(1)
    yield from asyncio.sleep(2)  # 遇到IO的操作的时候自动切换到task中的其他任务
    print(2)
    
@asyncio.coroutines
def fun6():
    print(3)
    yield from asyncio.sleep(2)  # 遇到IO的操作的时候自动切换到task中的其他任务
    print(4)

task = [
    asyncio.ensure_future(fun5()),
    asyncio.ensure_future(fun6())
]

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(task))

#显示结果
1
3
2
4

async & await关键字（py3.5）推荐的使用

import asyncio

async def fun7():
    print(7)
    await asyncio.sleep(2)  # 遇到IO的操作的时候自动切换到task中的其他任务
    print(8)

async def fun8():
    print(9)
    await asyncio.sleep(2)  # 遇到IO的操作的时候自动切换到task中的其他任务
    print(10)

task = [
    asyncio.ensure_future(fun7()),
    asyncio.ensure_future(fun8())
]

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(task))

图片下载实战

采用的普通方式进行图片的下载

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
@version: 1.0
@author: xjl
@file: 图片的下载.py
@time: 2021/9/12 16:49
"""
import requests

def download_images(url):
    print("开始下载", url)
    response = requests.get(url)
    print("下载完成")
    # 保存文件到本地中
    file_name = url.rsplit('_')[-1]
    with open(file_name, mode='wb') as file_object:
        file_object.writable(response.content)
    print("保存图片的功能完成")

if __name__ == "__main__":
    url_list = [
        'https://img.alicdn.com/imgextra/i3/127167800/O1CN01lywipS27US0reYkHE_!!0-saturn_solar.jpg_468x468q75.jpg',
        'https://img.alicdn.com/imgextra/i2/127167800/O1CN01M4cuWt27US1BH6Ke6_!!0-saturn_solar.jpg_468x468q75.jpg',
        'https://img.alicdn.com/imgextra/i4/206720011/O1CN01HKfJ251Bx53r6kuqZ_!!0-saturn_solar.jpg_468x468q75.jpg'
       ]
    for item in url_list:
        download_images(item)

采用的异步（协程的方式）方式进行图片的下载

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
@version: 1.0
@author: xjl
@file: 图片的下载异步操作.py
@time: 2021/9/12 17:04
"""

import aiohttp
import asyncio

async def fetch(session, url):
    print("发送请求")
    async with session.get(url, verify_ssl=False) as response:
        content = await response.content.read()
        file_name = url.rsplit('_')[-1]
        with open(file_name, mode='wb') as file_object:
            file_object.write(content)
        print("下载完成")

async def main():
    async with aiohttp.ClientSession() as session:
        url_list = [
            'https://img.alicdn.com/imgextra/i3/127167800/O1CN01lywipS27US0reYkHE_!!0-saturn_solar.jpg_468x468q75.jpg',
            'https://img.alicdn.com/imgextra/i2/127167800/O1CN01M4cuWt27US1BH6Ke6_!!0-saturn_solar.jpg_468x468q76.jpg',
            'https://img.alicdn.com/imgextra/i4/206720011/O1CN01HKfJ251Bx53r6kuqZ_!!0-saturn_solar.jpg_468x468q85.jpg'
        ]
        task = [asyncio.get_event_loop().create_task(fetch(session, url)) for url in url_list]
        await asyncio.wait(task)

if __name__ == '__main__':
    # asyncio.run(main()) 同文件夹下有 asyncio.py
    asyncio.get_event_loop().run_until_complete(main())

【路飞】Python异步编程2020年最新版【asyncio】【异步编程】【协程】_哔哩哔哩_bilibili