title: No kernel message on jupyterlab and jupyter notebook
body: <p>I have been using jupyter applications such as <code>jupyter-lab</code> and the <code>jupyter-notebook</code> for quite some time without any issues, but today I noticed a kernel problem while launching <code>jupyter-lab</code> from the command line or via the <code>anaconda-navigator</code> (I have installed <a href="https://www.anaconda.com/distribution/" rel="nofollow noreferrer">Anaconda with Python3.7 for Linux</a>).</p>
  
  <p>When I try to launch <code>jupyter-lab</code> via the command line, I get the following error messages (which also pop-up if I try to call <code>jupyter-lab</code> via anaconda navigator:</p>
  
  <pre><code>[I 16:37:07.486 LabApp] JupyterLab extension loaded from /home/user/anaconda3/lib/python3.7/site-packages/jupyterlab
  [I 16:37:07.486 LabApp] JupyterLab application directory is /home/user/anaconda3/share/jupyter/lab
  [W 16:37:07.487 LabApp] JupyterLab server extension not enabled, manually loading...
  [I 16:37:07.488 LabApp] JupyterLab extension loaded from /home/user/anaconda3/lib/python3.7/site-packages/jupyterlab
  [I 16:37:07.488 LabApp] JupyterLab application directory is /home/user/anaconda3/share/jupyter/lab
  [I 16:37:07.489 LabApp] Serving notebooks from local directory: /home/user
  [I 16:37:07.489 LabApp] The Jupyter Notebook is running at:
  [I 16:37:07.489 LabApp] http://localhost:8888/?token=b5912dbe9af5317da84389aaa05b8e96abd7e6402ec508ad
  [I 16:37:07.489 LabApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
  [C 16:37:07.503 LabApp] 
  
  To access the notebook, open this file in a browser:
  file:///run/user/17930/jupyter/nbserver-17066-open.html
  Or copy and paste one of these URLs:
  http://localhost:8888/?token=b5912dbe9af5317da84389aaa05b8e96abd7e6402ec508ad
  [I 16:37:09.485 LabApp] Node v8.15.0
  
  [I 16:37:09.620 LabApp] Build is up to date
  [I 16:37:10.026 LabApp] Kernel started: 7cc817c2-a48b-40bf-9721-c3401175a0e9
  Traceback (most recent call last):
  File "/home/user/anaconda3/lib/python3.7/runpy.py", line 193, in _run_module_as_main
  "__main__", mod_spec)
  File "/home/user/anaconda3/lib/python3.7/runpy.py", line 85, in _run_code
  exec(code, run_globals)
  File "/home/user/anaconda3/lib/python3.7/site-packages/ipykernel_launcher.py", line 15, in 
  from ipykernel import kernelapp as app
  File "/home/user/anaconda3/lib/python3.7/site-packages/ipykernel/__init__.py", line 2, in 
  from .connect import *
  File "/home/user/anaconda3/lib/python3.7/site-packages/ipykernel/connect.py", line 13, in 
  from IPython.core.profiledir import ProfileDir
  File "/home/user/anaconda3/lib/python3.7/site-packages/IPython/__init__.py", line 54, in 
  from .core.application import Application
  File "/home/user/anaconda3/lib/python3.7/site-packages/IPython/core/application.py", line 23, in 
  from traitlets.config.application import Application, catch_config_error
  File "/home/user/anaconda3/lib/python3.7/site-packages/traitlets/config/__init__.py", line 6, in 
  from .application import *
  File "/home/user/anaconda3/lib/python3.7/site-packages/traitlets/config/application.py", line 19, in 
  from traitlets.config.configurable import Configurable, SingletonConfigurable
  File "/home/user/anaconda3/lib/python3.7/site-packages/traitlets/config/configurable.py", line 12, in 
  from .loader import Config, LazyConfigValue, _is_section_key
  File "/home/user/anaconda3/lib/python3.7/site-packages/traitlets/config/loader.py", line 49, in 
  class ArgumentParser(argparse.ArgumentParser):
  AttributeError: module 'argparse' has no attribute 'ArgumentParser'
  </code></pre>
  
  <p>(then the computer tries to restart the kernel five times. After failing all five attempts to restart the kernel, the computer gives up and I see a <code>No kernel</code> on <code>jupyter-lab</code>)</p>
  
  <p>I am having a hard-time finding what the cause of the error can be because, as far as I recall, I did not make any change in any Python installation interpreter or anything like that. Also, other applications which were also installed via Anaconda, such as <code>Spyder</code>, are working normally.</p>
  
  <p>The only thing that I recall that I changed is that I added a manual proxy configuration for <code>Firefox</code>, which has always been my default browser. Nevertheless, I have set back the option to <code>No proxy</code> on <code>Firefox</code> and it does not work. Other than that, I get the very same problem if I set the default browser to <code>google chrome</code>.</p>
  
  <p>Does anyone </p>