title: Jupyter error: "No module named jupyter_core.paths"
body: <p>Trying to open Jupyter Notebook (OSX 10.11.4) I get the following error:</p>
  
  <pre><code>$ jupyter-notebook
  Traceback (most recent call last):
    File "/usr/local/bin/jupyter-notebook", line 7, in &lt;module&gt;
      from notebook.notebookapp import main
    File "/Users/geotheory/Library/Python/2.7/lib/python/site-packages/notebook/__init__.py", line 25, in &lt;module&gt;
      from .nbextensions import install_nbextension
    File "/Users/geotheory/Library/Python/2.7/lib/python/site-packages/notebook/nbextensions.py", line 23, in &lt;module&gt;
      from jupyter_core.paths import jupyter_data_dir, jupyter_path, SYSTEM_JUPYTER_PATH
  ImportError: No module named jupyter_core.paths
  </code></pre>
  
  <p>This used to work.  Any idea how to diagnose?</p>