arvoelke and xchoo - there was yet another problem which I think I resolved myself.
After incorporating all the suggested changes, I started nengo one more time and got more errors, ending with:
RuntimeError: The current Numpy installation ('c:\\users\\mark\\anaconda3\\envs\\nengo1-py3.7\\lib\\site-packages\\numpy\\__init__.py') fails to pass a sanity check due to a bug in the windows runtime. See this issue for more information: https://tinyurl.com/y3dm3h86
I went to the tinyurl link and found that there is a problem with numpy 1.19.4 on Windows 10 versions 2004 and 20H2. There may be a fix to Windows 10 sometime in January 2021, if I understand the link correctly. There are several possible temporary fixes. The one I tried involved reverting to numpy 1.19.3.
From my conda environment:
pip install numpy==1.19.3
I restarted my conda environment, started nengo, and things seemed to work.
To summarize:
(1) Installed Anaconda (Anaconda3-2020.11-Windows-x86_64.exe) on Windows 10 version 20H2.
(2) Within Anaconda, created an environment running Python 3.7:
create -n nengo1-py3.7 python=3.7
(3) Within my new nengo1-py3.7 environment, went back a level on numpy:
pip install numpy==1.19.3
(4) Did nengo install:
pip install "nengo<=3.0.0" nengo-gui
(5) I think I installed the jedi module at some point, based on other error messages. My brains were feeling a bit scrambled at this point.
(6) This is what I have in my nengo1-py3.7 environment:
Package Version ------------ ------------------- certifi 2020.12.5 jedi 0.17.2 nengo 3.0.0 nengo-gui 0.4.7 numpy 1.19.3 parso 0.7.1 pip 20.3.1 setuptools 51.0.0.post20201207 wheel 0.36.1 wincertstore 0.2
(7) Running nengo from my nengo1-py3.7 environment brings up a gui in my browser, usually with no error messages.
Thanks, people!