Don't die if template path cannot be read

[stuaxo]

Ordinary users may not have read access to conf in system directories,

In those cases .exists() will trigger a PermissionError when enumerating the conf directories.

[stuaxo]

This may be jupyter/jupyter#634

[takluyver]

Is this sufficient to avoid the problem you encountered? It looks like there are other exists() checks in get_template_names() which could also run into permission errors.

(It also seems weird to me that standard system directories under /usr wouldn't be readable, but I agree Jupyter should ideally cope with that, even if it's unusual)

[stuaxo]

It was sufficient for the bug I was seeing, it's certainly possible there could be other places with the same issue.

[stuaxo]

(I also found the fact .exists() can throw a permission error suprising, but it seems to be a thing.

[takluyver]

Fair enough. I'm just going to close & reopen this to re-run the tests with the fix from #2168.

It certainly can be surprising, but I think I prefer it to pretending inaccessible folders are empty; glob does behave like that, and I've certainly been caught by it before.

[stuaxo]

Cheers, I think this will help others who do what I did and combine homebrew and virtualenvs.