nbconvert `--user` install fails to find templates

[matthew-brett]

A completely default macOS --user install of Nbconvert fails with the following error:

$ python3 -m jupyter nbconvert foo.ipynb --to html
...
ValueError: No template sub-directory with name 'lab' found in the following paths:
	/Users/mbr110/Library/Jupyter
	/usr/local/opt/[email protected]/Frameworks/Python.framework/Versions/3.9/share/jupyter
	/usr/local/share/jupyter
	/usr/share/jupyter

I get the same error using Homebrew or Python.org Python.

Steps to reproduce:

• Make new user
• Put user bin directory on path: export PATH="$PATH:$HOME/Library/Python/3.9/bin" (needed for Jupyter subcommands to work);
• python3 -m pip install --user nbconvert
• touch foo.ipynb
• python3 -m jupyter nbconvert foo.ipynb --to html

This appears to be because Nbconvert is not looking in the default template install directory after a user install, which is (in my case, Python 3.9): ~/Library/Python/3.9/share/jupyter

https://stackoverflow.com/a/68294070

As the SO answer suggests, I can fix the error with a prior:

mkdir -p  ~/Library/Jupyter
ln -sf ~/Library/Python/3.9/share/jupyter/nbconvert ~/Library/Jupyter/nbconvert

I believe this is a bug, and that the macOS default user install directory should also be on the search path. Do y'all agree?

[dimpase]

It's not really a macOS-only bug. I see this in pyenv-installed environments on Linux, too. Cf. e.g. https://github.com/sagemath/sage/pull/36256#issuecomment-1721871688