【11.7】async和await

python3.5之后，才引入了原生协程的语法

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 
 4 # python为了将语义变得更加明确，就引入了async和await关键词用于定义原生的协程
 5 
 6 
 7 async def downloader(url):
 8     return 'zy'
 9 
10 
11 # 在async中不能yield，await只能出现在async中
12 async def download_url(url):
13     # do somethings
14     html = await downloader(url)
15 
16     return html
17 
18 
19 if __name__ == '__main__':
20     coro = download_url('http://www.imooc.com')
21     # next(coro)不能使用这种方式调用
22     coro.send(None)

Traceback (most recent call last):
  File "C:/Users/Administrator/Python/imooc/async_ts/async_await.py", line 22, in <module>
    coro.send(None)
StopIteration: zy