id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
32103	NotImplementedError in twisted (with Python 3.8 on Windows)	Andrey Zelenchuk	nobody	"The `runserver` management command does not work with Python ≥ 3.8 on Windows.

=== Steps to reproduce

1. Open any Django project.
2. Run `python manage.py runserver`.

==== Actual result

{{{
C:\Programs\Python38\python.exe C:/project/manage.py runserver
2020-10-11 18:12:08,823 INFO  [django.utils.autoreload] Watching for file changes with StatReloader
Exception in thread django-main-thread:
Traceback (most recent call last):
  File ""C:\Programs\Python38\lib\threading.py"", line 932, in _bootstrap_inner
    self.run()
  File ""C:\Programs\Python38\lib\threading.py"", line 870, in run
    self._target(*self._args, **self._kwargs)
  File ""C:\Programs\Python38\lib\site-packages\django\utils\autoreload.py"", line 53, in wrapper
    fn(*args, **kwargs)
  File ""C:\Programs\Python38\lib\site-packages\django\core\management\commands\runserver.py"", line 110, in inner_run
    autoreload.raise_last_exception()
  File ""C:\Programs\Python38\lib\site-packages\django\utils\autoreload.py"", line 76, in raise_last_exception
    raise _exception[1]
  File ""C:\Programs\Python38\lib\site-packages\django\core\management\__init__.py"", line 357, in execute
    autoreload.check_errors(django.setup)()
  File ""C:\Programs\Python38\lib\site-packages\django\utils\autoreload.py"", line 53, in wrapper
    fn(*args, **kwargs)
  File ""C:\Programs\Python38\lib\site-packages\django\__init__.py"", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File ""C:\Programs\Python38\lib\site-packages\django\apps\registry.py"", line 91, in populate
    app_config = AppConfig.create(entry)
  File ""C:\Programs\Python38\lib\site-packages\django\apps\config.py"", line 116, in create
    mod = import_module(mod_path)
  File ""C:\Programs\Python38\lib\importlib\__init__.py"", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File ""<frozen importlib._bootstrap>"", line 1014, in _gcd_import
  File ""<frozen importlib._bootstrap>"", line 991, in _find_and_load
  File ""<frozen importlib._bootstrap>"", line 975, in _find_and_load_unlocked
  File ""<frozen importlib._bootstrap>"", line 671, in _load_unlocked
  File ""<frozen importlib._bootstrap_external>"", line 783, in exec_module
  File ""<frozen importlib._bootstrap>"", line 219, in _call_with_frames_removed
  File ""C:\Programs\Python38\lib\site-packages\channels\apps.py"", line 6, in <module>
    import daphne.server
  File ""C:\Programs\Python38\lib\site-packages\daphne\server.py"", line 20, in <module>
    asyncioreactor.install(twisted_loop)
  File ""C:\Programs\Python38\lib\site-packages\twisted\internet\asyncioreactor.py"", line 320, in install
    reactor = AsyncioSelectorReactor(eventloop)
  File ""C:\Programs\Python38\lib\site-packages\twisted\internet\asyncioreactor.py"", line 69, in __init__
    super().__init__()
  File ""C:\Programs\Python38\lib\site-packages\twisted\internet\base.py"", line 571, in __init__
    self.installWaker()
  File ""C:\Programs\Python38\lib\site-packages\twisted\internet\posixbase.py"", line 286, in installWaker
    self.addReader(self.waker)
  File ""C:\Programs\Python38\lib\site-packages\twisted\internet\asyncioreactor.py"", line 151, in addReader
    self._asyncioEventloop.add_reader(fd, callWithLogger, reader,
  File ""C:\Programs\Python38\lib\asyncio\events.py"", line 501, in add_reader
    raise NotImplementedError
NotImplementedError
}}}

==== Expected result
No errors.

=== Workaround 
Add the following code to the `manage.py` file:
{{{
#!python
if sys.platform == 'win32' and sys.version_info >= (3, 8):
    import asyncio
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
}}}

=== References
- https://stackoverflow.com/questions/58908293/i-keep-getting-notimplementederror-error-when-starting-django-server"	Bug	closed	Core (Management commands)	3.1	Normal	invalid			Unreviewed	0	0	0	0	0	0