今天拉了一個使用了tornado的專案在本地跑，按照原始碼作者的步驟配置完，執行，直接報錯了，要求環境Python3.6+，我裝的是Python3.8，理論上應該直接正常執行的，報錯資訊：

Traceback (most recent call last):
File "ice_server.py",line 150,in <module>
RunServer.run_server(port=p,host=h)
File "ice_server.py",line 125,in run_server
tornado_server.start()
File "D:\PycharmProjects\ice\venv\lib\site-packages\tornado\tcpserver.py",line 244,in start

self.add_sockets(sockets)
File "D:\PycharmProjects\ice\venv\lib\site-packages\tornado\tcpserver.py",line 165,in add_sockets
self._handlers[sock.fileno()] = add_accept_handler(
File "D:\PycharmProjects\ice\venv\lib\site-packages\tornado\netutil.py",line 279,in add_accept_handler
io_loop.add_handler(sock,accept_handler,IOLoop.READ)

File "D:\PycharmProjects\ice\venv\lib\site-packages\tornado\platform\asyncio.py",line 100,in add_handler
self.asyncio_loop.add_reader(fd,self._handle_events,fd,IOLoop.READ)
File "C:\Users\huan\AppData\Local\Programs\Python\Python38\lib\asyncio\events.py",line 501,in add_reader
raise NotImplementedError

NotImplementedError

一番谷歌原來對於這個問題tornado的參與者們已經收到了很多反饋，有個回覆裡這麼說：

Python 3.8 asyncio is going to make the "proactor" event loop the default,instead of the current "selector" event loop. This is a problem for Tornado because the proactor event loop doesn't support the unix-style add_reader APIs that Tornado uses.

Anyone using Tornado 5+ on windows with python 3.8 will need to configure asyncio to use the selector event loop; we'll have to document this. We should also try to detect the use of a proactor event loop and give a clear error message

大概意思Python3.8的asyncio改變了迴圈方式，因為這種方式在windows上不支援相應的add_reader APIs，就會丟擲NotImplementedError錯誤。

解決辦法

找到這個專案使用的python環境的lib\site-packages，做下面的修改，在path-to-python\lib\site-packages\tornado\platform\asyncio.py開頭新增程式碼：

import sys

if sys.platform == 'win32':
  asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

這樣就可以正常運行了。

總結

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