title: IPython notebook kernel failed
body: <p>When I launch the ipython notebook in MacOSX El Capitan (10.11) and try to open an existing notebook, I get the following error when the kernel has been initiated:</p>
  
  <pre><code>[I 15:22:08.733 NotebookApp] Kernel started: 8e77535e-2af7-462d-9091-da5686de9a36
  /Library/Python/2.7/site-packages/jupyter_client/localinterfaces.py:242: UserWarning: Unexpected error discovering local network interfaces: insecure string pickle
    warn("Unexpected error discovering local network interfaces: %s" % e)
  [IPKernelApp] ERROR | Invalid Message
  Traceback (most recent call last):
    File "/Library/Python/2.7/site-packages/ipykernel/kernelbase.py", line 175, in dispatch_shell
      msg = self.session.deserialize(msg, content=True, copy=False)
    File "/Library/Python/2.7/site-packages/jupyter_client/session.py", line 870, in deserialize
      return adapt(message)
    File "/Library/Python/2.7/site-packages/jupyter_client/adapter.py", line 386, in adapt
      header['date'] = datetime.now().isoformat()
  NameError: global name 'datetime' is not defined
  [IPKernelApp] ERROR | Invalid Message
  Traceback (most recent call last):
    File "/Library/Python/2.7/site-packages/ipykernel/kernelbase.py", line 175, in dispatch_shell
      msg = self.session.deserialize(msg, content=True, copy=False)
    File "/Library/Python/2.7/site-packages/jupyter_client/session.py", line 870, in deserialize
      return adapt(message)
    File "/Library/Python/2.7/site-packages/jupyter_client/adapter.py", line 386, in adapt
      header['date'] = datetime.now().isoformat()
  NameError: global name 'datetime' is not defined
  </code></pre>
  
  <p>The kernel then dies...</p>
  
  <p>Any suggestions?</p>