python协程coroutine

从爬虫说起,这是一个同步方法

import time

def crawl_page(url):
    print('crawling {}'.format(url))
    sleep_time = int(url.split('_')[-1])
    time.sleep(sleep_time)
    print('OK {}'.format(url))

def main(urls):
    for url in urls:
        crawl_page(url)

%time main(['url_1', 'url_2', 'url_3', 'url_4'])

crawling url_1
OK url_1
crawling url_2
OK url_2
crawling url_3
OK url_3
crawling url_4
OK url_4
Wall time: 10.1 s

nest_asyncio模块允许在已经有一个运行中的事件循环的环境（如 Jupyter Notebook）中使用asyncio.run()。

!pip install nest_asyncio

Collecting nest_asyncio
  Downloading https://files.pythonhosted.org/packages/a0/c4/c2971a3ba4c6103a3d10c4b0f24f461ddc027f0f09763220cf35ca1401b3/nest_asyncio-1.6.0-py3-none-any.whl
Installing collected packages: nest-asyncio
Successfully installed nest-asyncio-1.6.0


WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ReadTimeoutError("HTTPSConnectionPool(host='pypi.org', port=443): Read timed out. (read timeout=15)")': /simple/nest-asyncio/
WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x000001F1788907F0>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/nest-asyncio/

这样，你就大概看懂了协程是怎么用的吧。不妨试着跑一下代码，欸，怎么还是 10 秒？

import asyncio
import nest_asyncio

# 允许在 Jupyter Notebook 中运行 asyncio.run()
nest_asyncio.apply()

async def crawl_page(url):
    print('crawling {}'.format(url))
    sleep_time = int(url.split('_')[-1])
    await asyncio.sleep(sleep_time)
    print('OK {}'.format(url))

async def main(urls):
    for url in urls:
        await crawl_page(url)

%time asyncio.run(main(['url_1', 'url_2', 'url_3', 'url_4']))

crawling url_1
OK url_1
crawling url_2
OK url_2
crawling url_3
OK url_3
crawling url_4
OK url_4
Wall time: 10.1 s

接下来要讲的协程中的一个重要概念，任务（Task）

import asyncio

async def crawl_page(url):
    print('crawling {}'.format(url))
    sleep_time = int(url.split('_')[-1])
    await asyncio