Note: this issue is fixed in Spyder 4.1.3!

(original question) checking out Python 3.8 (x64) on Windows 10, I got into trouble when trying to setup Spyder. Note: the issue was reproducible with a fresh Python installation on a clean Windows-10 system. However, no such issues on Linux (tested on debian / Mint19.x).

At first, everything went smooth during installation via pip install spyder.

error #1: pywin32

After starting Spyder, it said in the IPython console window:

Traceback (most recent call last):
File "c:\users\USERNAME\appdata\local\programs\python\python38\lib\site‑packages\spyder\plugins\ipythonconsole.py", line 1572, in create_kernel_manager_and_kernel_client
kernel_manager.start_kernel(stderr=stderr_handle)
File "c:\users\USERNAME\appdata\local\programs\python\python38\lib\site‑packages\jupyter_client\manager.py", line 240, in start_kernel
self.write_connection_file()
File "c:\users\USERNAME\appdata\local\programs\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:\users\USERNAME\appdata\local\programs\python\python38\lib\site‑packages\jupyter_client\connect.py", line 141, in write_connection_file
with secure_write(fname) as f:
File "c:\users\USERNAME\appdata\local\programs\python\python38\lib\contextlib.py", line 113, in __enter__
return next(self.gen)
File "c:\users\USERNAME\appdata\local\programs\python\python38\lib\site‑packages\jupyter_core\paths.py", line 424, in secure_write
win32_restrict_file_to_user(fname)
File "c:\users\USERNAME\appdata\local\programs\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: Das angegebene Modul wurde nicht gefunden.

I was able to fix the import error by running pywin32_postinstall.py -install from the scripts folder (from a cmd prompt with elevated rights). That copies pythoncom38.dll and pywintypes38.dll from \Lib\site-packages\pywin32_system32 to \windows\system32, see also here - however, I'd suggest to not modify system folders and use the option I put in my answer below.

error #2: tornado

However, now Spyder just freezes at the loading screen (logo displayed, saying something like "initializing main window")!

cloning the dev version of Spyder from https://github.com/spyder-ide/spyder.git and running it via python bootstrap.py --debug reveals the cause of the freeze:

2019-11-03 17:39:53,261 [ERROR] [tornado.application] -> Exception in callback functools.partial(<function ThreadedZMQSocketChannel.__init__.<locals>.setup_stream at 0x0000015E00B758B0>)
Traceback (most recent call last):
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\site-packages\tornado\ioloop.py", line 743, in _run_callback
    ret = callback()
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\site-packages\jupyter_client\threaded.py", line 48, in setup_stream
    self.stream = zmqstream.ZMQStream(self.socket, self.ioloop)
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\site-packages\zmq\eventloop\zmqstream.py", line 127, in __init__
    self._init_io_state()
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\site-packages\zmq\eventloop\zmqstream.py", line 546, in _init_io_state
    self.io_loop.add_handler(self.socket, self._handle_events, self.io_loop.READ)
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\site-packages\tornado\platform\asyncio.py", line 99, in add_handler
    self.asyncio_loop.add_reader(fd, self._handle_events, fd, IOLoop.READ)
  File "C:\Users\USERNAME\AppData\Local\Programs\Python\Python38\lib\asyncio\events.py", line 501, in add_reader
    raise NotImplementedError
NotImplementedError

...so it seems the import error caused by the Python 3.8 version of pywin32 is only one issue. There's also a problem related to tornado IO (web server), see here / here.

last checked with Python 3.8.2 (AMD64), Spyder 4.1.1. Please note that I am not using Anaconda. Use either conda or pip, not both.

Spyder 4.1.3 Update: The issue is fixed!

(Tested on Python 3.8.3rc1, tornado 6.0.4)

If you come here still experiencing similar startup issues with Spyder: the first thing to try I'd suggest upgrade to Spyder version >= 4.1.3.

older version of this answer

workaround, tornado issue:

Modify the file ...\Python38...\Lib\site-packages\tornado\platform\asyncio.py; add

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

after the other import statements. Source: here on SO and also linked here. If I get this post on the tornado repo right, this is likely to be a pretty permanent workaround.

if also needed - workaround, pywin32 issue:

Modify the file ...\Python38\Lib\site-packages\jupyter_core\path.py; add a line

import pywintypes

before import win32api in line 359. This modification is based on this post.

Note: this issue is fixed in Spyder 4.1.3!

Spyder 4.1.3 Update: The issue is fixed!

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