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Python3 Tornado in Windows

Python3 Tornado in Windows

How to fix the NoImplementedError in asyncio.py

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Alessandro
·

1 min read

This all starts with the best intentions… you install python 3, the tornado libraries follow, and finally once you complete your first tornado web application and test it you get the following:

alt error_tornado_windows.png

Well then to fix this issue you need to do the following:

import concurrent.futures
import functools

from threading import get_ident
from tornado.gen import convert_yielded
from tornado.ioloop import IOLoop, _Selectable

import asyncio

# Start of fix for Windows
import sys

if sys.platform == 'win32':
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
# End of fix

import typing
from typing import Any, TypeVar, Awaitable, Callable, Union, Optional

if typing.TYPE_CHECKING:
    from typing import Set, Dict, Tuple  # noqa: F401

_T = TypeVar("_T")

Seems like the later version of tornado, in windows only, have a missing implementation error on the event loop policy. So you need to add the win32 if statement and import the sys library to your asyncio.py file located in the following folder: \Python38\Lib\site-packages\tornado\platform

Now you should be set ;-)

Python 3PythonWindowsservererror