title: Plotly Dash application not running
body: <p>I am attempting to run the following code from jupyter notebook:</p>
  
  <pre><code>import dash
  import dash_core_components as dcc
  import dash_html_components as html
  
  external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']
  
  app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
  
  app.layout = html.Div(children=[
      html.H1(children='Hello Dash'),
  
      html.Div(children='''
          Dash: A web application framework for Python.
      '''),
  
      dcc.Graph(
          id='example-graph',
          figure={
              'data': [
                  {'x': [1, 2, 3], 'y': [4, 1, 2], 'type': 'bar', 'name': 'SF'},
                  {'x': [1, 2, 3], 'y': [2, 4, 5], 'type': 'bar', 'name': u'Montréal'},
              ],
              'layout': {
                  'title': 'Dash Data Visualization'
              }
          }
      )
  ])
  
  if __name__ == '__main__':
      app.run_server(debug=True)
  </code></pre>
  
  <p>It produces the following: </p>
  
  <pre><code> * Serving Flask app "__main__" (lazy loading)
   * Environment: production
     WARNING: This is a development server. Do not use it in a production deployment.
     Use a production WSGI server instead.
   * Debug mode: on
   * Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)
   * Restarting with stat
  An exception has occurred, use %tb to see the full traceback.
  
  SystemExit: 1
  
  
  //anaconda3/lib/python3.7/site-packages/IPython/core/interactiveshell.py:3333: UserWarning:
  
  To exit: use 'exit', 'quit', or Ctrl-D.
  </code></pre>
  
  <p>When I click on <a href="http://127.0.0.1:8050/" rel="noreferrer">http://127.0.0.1:8050/</a> , the page never loads.  I've been trying this for awhile now. Is there something in the response that I am missing?  This should be a basic dash application. </p>
  
  <p>Here is the traceback: </p>
  
  <pre><code>---------------------------------------------------------------------------
  SystemExit                                Traceback (most recent call last)
  &lt;ipython-input-1-b057c246c3cf&gt; in &lt;module&gt;
       29 
       30 if __name__ == '__main__':
  ---&gt; 31     app.run_server(debug=True)
       32 
       33 get_ipython().run_line_magic('tb', '')
  
  //anaconda3/lib/python3.7/site-packages/dash/dash.py in run_server(self, port, debug, **flask_run_options)
      566                    debug=False,
      567                    **flask_run_options):
  --&gt; 568         self.server.run(port=port, debug=debug, **flask_run_options)
  
  //anaconda3/lib/python3.7/site-packages/flask/app.py in run(self, host, port, debug, load_dotenv, **options)
      988 
      989         try:
  --&gt; 990             run_simple(host, port, self, **options)
      991         finally:
      992             # reset the first request information if the development server
  
  //anaconda3/lib/python3.7/site-packages/werkzeug/serving.py in run_simple(hostname, port, application, use_reloader, use_debugger, use_evalex, extra_files, reloader_interval, reloader_type, threaded, processes, request_handler, static_files, passthrough_errors, ssl_context)
     1005         from ._reloader import run_with_reloader
     1006 
  -&gt; 1007         run_with_reloader(inner, extra_files, reloader_interval, reloader_type)
     1008     else:
     1009         inner()
  
  //anaconda3/lib/python3.7/site-packages/werkzeug/_reloader.py in run_with_reloader(main_func, extra_files, interval, reloader_type)
      330             reloader.run()
      331         else:
  --&gt; 332             sys.exit(reloader.restart_with_reloader())
      333     except KeyboardInterrupt:
      334         pass
  
  SystemExit: 1
  </code></pre>