异步协程-class01

• 协程
• asyncio模块进行异步编程
• 实战案例

1.协程

协程不是计算机提供，程序员人为创造。
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的技术，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。

实现协程的方法:

• greenlet, 早期模块
• yield关键字
• asyncio装饰器（py3.4引入）
• async、await关键字（py3.5）【推荐】

1.1 greenlet实现协程

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from greenlet import greenlet

def func1():
	print(1)	# 第二步：输出1
   gr2.switch()	# 第三步：切换到func2
   print(2)		# 第六步：输出2
   gr2.switch()	# 第七步：切换到func2
 
def func2():
	print(3)	# 第四步：输出3
   gr1.switch()	# 第五步：切换到func1
   print(4)		# 第八步：输出4
   

gr1 = greenlet(func1)
gr2 = greenlet(func2)

gr1.switch()	# 第一步：切换到func1

输出结果

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4

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2
4

1.2 yield关键字

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def func1():
    yield 1
    yield from func2()
    yield 2


def func2():
    yield 3
    yield 4


f1 = func1()
for item in f1:
    print(item)

输出结果

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4

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4
2

1.3 async、await关键字

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import asyncio

async def func1():
   print(1)
   await asyncio.sleep(2)
   print(2)
   
async def func2():
   print(3)
   await asyncio.sleep(2)
   print(4)
   
tasks = [
   asyncio.ensure_future(func1()),
   asyncio.ensure_future(func2())
]

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

__注意：遇到IO阻塞自动切换
输出结果

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5

1
3
--------停顿
2
4

协程的意义

在线程中如果遇到IO等待时间，线程可利用空闲时间干其他的事情

2.1 案例：下载三张图片

• 普通方式

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  import request import time def download(url): name = url.rsplit("/", 1)[1] res = requests.get(url) with open(name, mode="wb") as f: f.write(res.content)   print(name + "Finish.") if "__name__" == "__main__": url_list = [ "https://img-baofun.zhhainiao.com/pcwallpaper_ugc/preview/3760b2031ff41ca0bd80bc7a8a13f7bb_preview.mp4", "https://img-baofun.zhhainiao.com/market/97ba6b60662ab4f31ef06cdf5a5f8e94_preview.mp4", "https://wallpaperm.cmcm.com/scene/preview_video/750c4e56cb120056c9d155b63025c564_preview.mp4" ] start = time.time() for i in url_list: download(i) stop = time.time() print(stop - start)

• 协程方式

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  import asyncio import aiohttp import time async def download(session, url): async with session.get(url) as response: content = response.content.read() file_name = url.rsplit("/", 1)[1] with open(file_name, mode="wb") as f: f.write(content) print(file_name + " " +"done") async def main(): async with aiohttp.ClientSession as session: url_list = [ "https://img-baofun.zhhainiao.com/pcwallpaper_ugc/preview/3760b2031ff41ca0bd80bc7a8a13f7bb_preview.mp4", "https://img-baofun.zhhainiao.com/market/97ba6b60662ab4f31ef06cdf5a5f8e94_preview.mp4", "https://wallpaperm.cmcm.com/scene/preview_video/750c4e56cb120056c9d155b63025c564_preview.mp4" ] taaks = [asyncio.creat_task(download(session, url)) for url in url_list] await async.wait(tasks) if "__name__" == "__main__": start = time.time() loop = asyncio.get_event_loop() loop.run_until_complete(main()) stop = time.time() print(stop - start)

  done