Improve error handling when .jupyter is a file instead of directory

[willingc]

While troubleshooting an issue on Cal Poly's JupyterHub deployment (https://github.com/jupyterhub/jupyterhub/issues/1618), we found that the notebook server can't start if ~/.jupyter is a file. Filing a follow up issue here as this error probably effects all Jupyter entrypoints. The relevant code is likely in this repo's source.

cc/ @minrk @ellisonbg

[ellisonbg]

A few more details:

• This issue showed up in a jupyterhub deployment when I asked users to configure an nbgrader_config.py file in .jupyter.
• Some of the users accidentally created a .jupyter file rather than a directory

On Thu, Jan 11, 2018 at 12:30 PM, Carol Willing [email protected] wrote:

While troubleshooting an issue on Cal Poly's JupyterHub deployment ( jupyterhub/jupyterhub#1618 https://github.com/jupyterhub/jupyterhub/issues/1618), we found that the notebook server can't start if ~/.jupyter is a file. Filing a follow up issue here as this error probably effects all Jupyter entrypoints. The relevant code is likely in this repo's source.

cc/ @minrk https://github.com/minrk @ellisonbg https://github.com/ellisonbg

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-- Brian E. Granger Associate Professor of Physics and Data Science Cal Poly State University, San Luis Obispo @ellisonbg on Twitter and GitHub [email protected] and [email protected]