[Python 3.8][Windows 10] Kernel error after opening notebook file (Tornado manually patched to return to selector event loop)

[indeets-vasily]

I have Python 3.8.0 on windows 10 x86-64.

At first Jupyter console was throwin NotImplementedError. After searching web I applied patches suggested there:
https://stackoverflow.com/questions/58422817/jupyter-notebook-with-python-3-8-notimplementederror
https://stackoverflow.com/questions/54805213/jupyter-notebook-cannot-start-with-python-3-8-in-windows-10

Basically, I added following strings to /tornado/platform/asyncio.py:

import sys

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

After applying this change I don't get NotImplementedError and I see list of files/directories on my computer in the web browser. But when I open notebook file I see Kernel Error and have following output in the console:

[E 22:27:23.239 NotebookApp] Uncaught exception POST /api/sessions (127.0.0.1)
    HTTPServerRequest(protocol='http', host='localhost:8888', method='POST', uri='/api/sessions', version='HTTP/1.1', remote_ip='127.0.0.1')
    Traceback (most recent call last):
      File "c:\python\python38\lib\site-packages\tornado\web.py", line 1699, in _execute
        result = await result
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 742, in run
        yielded = self.gen.throw(*exc_info)  # type: ignore
      File "c:\python\python38\lib\site-packages\notebook\services\sessions\handlers.py", line 69, in post
        model = yield maybe_future(
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 735, in run
        value = future.result()
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 742, in run
        yielded = self.gen.throw(*exc_info)  # type: ignore
      File "c:\python\python38\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 88, in create_session
        kernel_id = yield self.start_kernel_for_session(session_id, path, name, type, kernel_name)
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 735, in run
        value = future.result()
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 742, in run
        yielded = self.gen.throw(*exc_info)  # type: ignore
      File "c:\python\python38\lib\site-packages\notebook\services\sessions\sessionmanager.py", line 100, in start_kernel_for_session
        kernel_id = yield maybe_future(
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 735, in run
        value = future.result()
      File "c:\python\python38\lib\site-packages\tornado\gen.py", line 209, in wrapper
        yielded = next(result)
      File "c:\python\python38\lib\site-packages\notebook\services\kernels\kernelmanager.py", line 168, in start_kernel
        super(MappingKernelManager, self).start_kernel(**kwargs)
      File "c:\python\python38\lib\site-packages\jupyter_client\multikernelmanager.py", line 110, in start_kernel
        km.start_kernel(**kwargs)
      File "c:\python\python38\lib\site-packages\jupyter_client\manager.py", line 240, in start_kernel
        self.write_connection_file()
      File "c:\python\python38\lib\site-packages\jupyter_client\connect.py", line 470, in write_connection_file
        self.connection_file, cfg = write_connection_file(self.connection_file,
      File "c:\python\python38\lib\site-packages\jupyter_client\connect.py", line 141, in write_connection_file
        with secure_write(fname) as f:
      File "c:\python\python38\lib\contextlib.py", line 113, in __enter__
        return next(self.gen)
      File "c:\python\python38\lib\site-packages\jupyter_core\paths.py", line 424, in secure_write
        win32_restrict_file_to_user(fname)
      File "c:\python\python38\lib\site-packages\jupyter_core\paths.py", line 359, in win32_restrict_file_to_user
        import win32api
    ImportError: DLL load failed while importing win32api: The specified module could not be found.
[W 22:27:23.239 NotebookApp] Unhandled error
[E 22:27:23.239 NotebookApp] {
      "Host": "localhost:8888",
      "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:70.0) Gecko/20100101 Firefox/70.0",
      "Accept": "application/json, text/javascript, */*; q=0.01",
      "Accept-Language": "en-US,en;q=0.5",
      "Accept-Encoding": "gzip, deflate",
      "Content-Type": "application/json",
      "X-Xsrftoken": "2|5b5eff67|0db0eda37f66596ea26522cfad762e4c|1573142996",
      "X-Requested-With": "XMLHttpRequest",
      "Content-Length": "102",
      "Origin": "http://localhost:8888",
      "Connection": "keep-alive",
      "Referer": "http://localhost:8888/notebooks/watch%20shop/Untitled.ipynb",
      "Cookie": "username-localhost-8888=\"2|1:0|10:1573248432|23:username-localhost-8888|44:ZGU2ZTFiZWFkNzQzNDRiN2IwOWI4ZGIzYjAxY2Y0ZDM=|da23157c2eb09136be584ce85e512a75a8cb5d3b74b1037fc9f1b5698e81182b\"; _xsrf=2|5b5eff67|0db0eda37f66596ea26522cfad762e4c|1573142996"
    }
[E 22:27:23.239 NotebookApp] 500 POST /api/sessions (127.0.0.1) 62.49ms referer=http://localhost:8888/notebooks/watch%20shop/Untitled.ipynb

[afvca]

See this #4980 (comment)

[indeets-vasily]

It worked, thanks!