第二章 协程的意义

2.协程意义

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。

案例：去下载三张图片（网络IO）。

• 普通方式（同步）

  """ pip3 install requests """
  
  import requests
  
  
  def download_image(url):
  	print("开始下载:",url)
      # 发送网络请求，下载图片
      response = requests.get(url)
  	print("下载完成")
      # 图片保存到本地文件
      file_name = url.rsplit('_')[-1]
      with open(file_name, mode='wb') as file_object:
          file_object.write(response.content)
  
  
  if __name__ == '__main__':
      url_list = [
          'https://www3.autoimg.cn/newsdfs/g26/M02/35/A9/120x90_0_autohomecar__ChsEe12AXQ6AOOH_AAFocMs8nzU621.jpg',
          'https://www2.autoimg.cn/newsdfs/g30/M01/3C/E2/120x90_0_autohomecar__ChcCSV2BBICAUntfAADjJFd6800429.jpg',
          'https://www3.autoimg.cn/newsdfs/g26/M0B/3C/65/120x90_0_autohomecar__ChcCP12BFCmAIO83AAGq7vK0sGY193.jpg'
      ]
      for item in url_list:
          download_image(item)
  

• 协程方式（异步）

  """
  下载图片使用第三方模块aiohttp，请提前安装：pip3 install aiohttp
  """
  #!/usr/bin/env python
  # -*- coding:utf-8 -*-
  import aiohttp
  import asyncio
  
  
  async def fetch(session, url):
      print("发送请求：", url)
      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',url)
  
  async def main():
      async with aiohttp.ClientSession() as session:
          url_list = [
              'https://www3.autoimg.cn/newsdfs/g26/M02/35/A9/120x90_0_autohomecar__ChsEe12AXQ6AOOH_AAFocMs8nzU621.jpg',
              'https://www2.autoimg.cn/newsdfs/g30/M01/3C/E2/120x90_0_autohomecar__ChcCSV2BBICAUntfAADjJFd6800429.jpg',
              'https://www3.autoimg.cn/newsdfs/g26/M0B/3C/65/120x90_0_autohomecar__ChcCP12BFCmAIO83AAGq7vK0sGY193.jpg'
          ]
          tasks = [ asyncio.create_task(fetch(session, url)) for url in url_list ]
  
          await asyncio.wait(tasks)
  
  
  if __name__ == '__main__':
      asyncio.run( main() )