Add site user base directory to config and data paths if site.ENABLE_USER_SITE is true

[jasongrout]

This allows someone to install Jupyter components in the Python user directory (for example, with pip install —user) and Jupyter will see them. It seems like a natural extension of our user-level directories.

Fixes #221

@minrk - I'm curious what you think of this change.

[jasongrout]

Setting as draft since we should add better tests and documentation (for example, how to disable this directory by setting the PYTHONNOUSERSITE variable or calling python with -s, etc.).

[minrk]

@jasongrout I just had an occasion where I almost made this PR myself, so 👍 from me.

[jasongrout]

Thanks for your review, Min! I added tests, docs, and a note in the --debug printout.

[jasongrout]

@minrk - if my polishing additions look good to you, can you merge? Thanks!

[vidartf]

@jasongrout I see there was a comment about duplicates in data? Is that expected?

[vidartf]

AFAICT, the duplicate comes from this logic that is only applied to data dirs:

jupyter_core/jupyter_core/paths.py

Lines 90 to 102 in 6de55f5

	if sys.platform == 'darwin':
	return os.path.join(home, 'Library', 'Jupyter')
	elif os.name == 'nt':
	appdata = os.environ.get('APPDATA', None)
	if appdata:
	return str(Path(appdata, 'jupyter').resolve())
	else:
	return pjoin(jupyter_config_dir(), 'data')
	else:
	# Linux, non-OS X Unix, AIX, etc.
	xdg = env.get("XDG_DATA_HOME", None)
	if not xdg:
	xdg = pjoin(home, '.local', 'share')

Does this logic overlap partially/fully with that of site.getuserbase() ?

[jasongrout]

It appears that the code path is if %APPDATA% is defined to be the home .local directory, then we see that duplicate? I'm not sure if it is coincidence or not that the user base directory appears to also be that same directory.

We can at least check for a duplicate and not add the directory if there would be a duplicate. That would at least avoid the issue of having to look twice in the same directory.

[jasongrout]

We can at least check for a duplicate and not add the directory if there would be a duplicate. That would at least avoid the issue of having to look twice in the same directory.

Done in 7a8e44c

[minrk]

Thanks!

[jasongrout]

Thanks everyone!

I'll make an RC for 4.9 with this PR, targeting a release for next week.

[jasongrout]

I just released 4.9.0 to pypi.