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python 异步编程——asyncio

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python 異步編程——asyncio

摘要
1. 協(xié)程
- 1.1 基本概念
- 1.2 實現(xiàn)方法
- - 1.2.1 greenlet
  - 1.2.2 yield
  - 1.2.3 asyncio模塊
  - 1.2.4 async、await關鍵字（推薦）
  - 1.2.5 協(xié)程的意義
2. 異步編程（asyncio模塊）
- 2.1 事件循環(huán)
- - 2.1.1 定義
- 2.2 協(xié)程函數(shù)（async關鍵字） & 攜程對象
- 2.3 await關鍵字
- 2.4 Task對象
- 2.5 future 對象
- 2.6 concurrent.futures.Future對象
- 2.7 異步迭代器
- 2.8 異步上下文管理器
3. uvloop
4. 案例
- 4.1 連接MySQL
- 4.2 FastAPI框架

摘要

本文主要介紹了python通過asyncio模塊如何實現(xiàn)異步編程。

1. 協(xié)程

1.1 基本概念

協(xié)程不是計算機提供的，程序員人為創(chuàng)造；

協(xié)程（coroutine，微線程），即一個線程實現(xiàn)代碼塊相互切換執(zhí)行；

1.2 實現(xiàn)方法

greenlet模塊（早期）

yield關鍵字

asyncio模塊（py3.4）

async、await關鍵字（py3.5）

1.2.1 greenlet

pip install greenlet from greenlet import greenlet def func_a():print("first in func_a!")gr_b.switch()print("second in func_a!")gr_b.switch()print("third in func_a!")gr_b.switch()def func_b():print("first in func_b!")gr_a.switch()print("second in func_b!")gr_a.switch()print("third in func_b!")gr_a = greenlet(func_a) gr_b = greenlet(func_b)gr_a.switch() first in func_a! first in func_b! second in func_a! second in func_b! third in func_a! third in func_b!

1.2.2 yield

def func_a():yield "first in func_a!"yield from func_b()yield "second in func_a!"yield "third in func_a!"def func_b():yield "first in func_b!"yield "second in func_b!"yield "third in func_b!" iters = func_a() for i in iters:print(i) first in func_a! first in func_b! second in func_b! third in func_b! second in func_a! third in func_a!

1.2.3 asyncio模塊

import asyncio@asyncio.coroutine def func_a():print("first in func_a!")yield from asyncio.sleep(2)print("second in func_a!")yield from asyncio.sleep(2)print("third in func_a!")@asyncio.coroutine def func_b():print("first in func_b!")yield from asyncio.sleep(2)print("second in func_b!")yield from asyncio.sleep(2)print("third in func_b!")tasks = [asyncio.ensure_future(func_a()),asyncio.ensure_future(func_b())] loop = asyncio.get_event_loop() loop.run_until_complete(asyncio.wait(tasks)) first in func_a! first in func_b! second in func_a! second in func_b! third in func_a! third in func_b!

1.2.4 async、await關鍵字（推薦）

import asyncioasync def func_a():print("first in func_a!")await asyncio.sleep(2)print("second in func_a!")await asyncio.sleep(2)print("third in func_a!")async def func_b():print("first in func_b!")await asyncio.sleep(2)print("second in func_b!")await asyncio.sleep(2)print("third in func_b!")tasks = [asyncio.ensure_future(func_a()),asyncio.ensure_future(func_b())] loop = asyncio.get_event_loop() loop.run_until_complete(asyncio.wait(tasks)) first in func_a! first in func_b! second in func_a! second in func_b! third in func_a! third in func_b!

1.2.5 協(xié)程的意義

在一個線程中，如果遇到IO等待時間，利用該空閑時間去處理其余任務。

2. 異步編程（asyncio模塊）

2.1 事件循環(huán)

2.1.1 定義

死循環(huán)：檢測并執(zhí)行某些代碼。

import asyncio# 獲取一個事件循環(huán) loop = asyncio.get_event_loop() #將任務放到任務列表 loop.run_until_complete(tasks)

2.2 協(xié)程函數(shù)（async關鍵字） & 攜程對象

協(xié)程函數(shù) async def 函數(shù)名攜程對象執(zhí)行攜程函數(shù)得到的對象 func() async func():pass result = func() # 得到協(xié)程對象時，函數(shù)內部代碼不會執(zhí)行。

執(zhí)行協(xié)程對象

import asyncio async def func():pass asyncio.run(func())

2.3 await關鍵字

await 后接可等待的對象（協(xié)程對象、Future對象、Task對象）即IO等待# 舉例1 import asyncio async def func():print("開始執(zhí)行！")response = await asyncio.sleep(2)print("已結束！",response) asyncio.run(func())# 舉例2 import asyncioasync def fun_a():print("func_a:1!")await asyncio.sleep(2)print("func_a:2!")return "func_a:over!"async def fun_b():print("func_b:1")response = await fun_a()print(response)asyncio.run(fun_b())結果為： func_b:1 func_a:1! func_a:2! func_a:over!

2.4 Task對象

在事件循環(huán)中添加多個任務。

Task用于并發(fā)調度協(xié)程， asyncio.create_task(協(xié)程對象) import asyncioasync def fun_a():print("func_a:1!")await asyncio.sleep(2)print("func_a:2!")return "func_a:over!"async def fun_b():print("func_b:1")tasks = [asyncio.create_task(fun_a()),asyncio.create_task(fun_a()),]done,pending = await asyncio.wait(tasks)print(done)asyncio.run(fun_b()) func_b:1 func_a:1! func_a:1! func_a:2! func_a:2!

2.5 future 對象

Task繼承Future對象，Task的await結果由Future處理而來。（很少使用）

2.6 concurrent.futures.Future對象

使用進程池或線程池實現(xiàn)異步操作。

from concurrent.futures import Future from concurrent.futures.thread import ThreadPoolExecutor from concurrent.futures.process import ProcessPoolExecutordef func(val):print(val)return valthread_pool = ThreadPoolExecutor(max_workers=5)for i in range(10):fut = thread_pool.submit(func,i)print(fut)

協(xié)程與線程（進程）的交叉使用

import asyncio from concurrent.futures import Future from concurrent.futures.thread import ThreadPoolExecutor from concurrent.futures.process import ProcessPoolExecutorasync def func_a():print("func_a:1!")await asyncio.sleep(2)print("func_a:2!")return 200def func_b(val):print(val)print("I am in func_b!")return 100async def main():print("main func:1!")result = await func_a()print(result)loop = asyncio.get_running_loop()# 1、使用線程調用func_bfuture = loop.run_in_executor(None,func_b,2011)# # 2、使用線程調用func_b# with ThreadPoolExecutor(max_workers=5) as executor:# future = loop.run_in_executor(executor, func_b, 2011)## # 3、使用進程調用func_b# with ProcessPoolExecutor(max_workers=5) as executor:# future = loop.run_in_executor(executor, func_b, 2011)response = await futureprint(response)asyncio.run(main()) main func:1! func_a:1! func_a:2! 200 2011 I am in func_b! 100

案例（asyncio+不支持異步的模塊）

// An highlighted block import asyncio from concurrent.futures.thread import ThreadPoolExecutor import requests import randomasync def spider(url):loop = asyncio.get_running_loop()print("start to download {}".format(url))with ThreadPoolExecutor(max_workers=5) as executor:result = loop.run_in_executor(executor,requests.get,url)response = await resultprint("end to download {}".format(url))with open("{}.png".format(random.choice([i for i in range(1000)])),"wb") as f:f.write(response.content)urls = 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m%2Fimages%2F20181103%2Fac15613329de46099b3bc0d5398ff9ea.jpeg%26refer%3Dhttp%3A%2F%2F5b0988e595225.cdn.sohucs.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1644734709%26t%3D60e503e73c3c9a23d100ebd435e17c48&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bf5i7_z%26e3Bv54AzdH3FwAzdH3Fd0dlcmamd_m09baa&gsm=26&rpstart=0&rpnum=0&islist=&querylist=&nojc=undefined&dyTabStr=MCwzLDEsNiw0LDIsNSw3LDgsOQ%3D%3D",]task = [spider(url) for url in urls]asyncio.run(asyncio.wait(task))

2.7 異步迭代器

不常用

2.8 異步上下文管理器

import asyncio async def main():async with AsyncManager() as f:f.do_sth() asyncio.run(main())

3. uvloop

使用uvloop替代asyncio的默認事件循環(huán)，效率高出兩倍 pip install uvloopimport asyncio import uvloop asyncion.set_event_loop_policy(uvloop.EventLoopPolicy())

4. 案例

4.1 連接MySQL

pip insatll aiomysql

4.2 FastAPI框架

pip insatll fastapi pip insatll uvicorn

by CyrusMay 2022 01 14

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