title: Flask app not connecting to the port
body: <p>I'm following the Flask Web Development Tutorial by Miguel Grinberg, and I've copied this code </p>
  
  <pre><code>from flask import Flask
  app = Flask(__name__)
  @app.route('/')
  def index():
      return '&lt;h1&gt;Hello World!&lt;/h1&gt;'
  if __name__ == '__main__':
      app.run(debug=True)
  </code></pre>
  
  <p>And on Jupyter I get this result: 
   * Running on <a href="http://127.0.0.1:5000/" rel="nofollow noreferrer">http://127.0.0.1:5000/</a> (Press CTRL+C to quit)
   * Restarting with stat
  An exception has occurred, use %tb to see the full traceback.
  SystemExit: 1</p>
  
  <p>If I open <a href="http://127.0.0.1:5000/" rel="nofollow noreferrer">http://127.0.0.1:5000/</a> the page is just loading forever, same thing if I run the code on the Powershell (but without giving the error).
  I've tried to look for similar questions but I wasn't able to find something, can you please tell me what I'm doing wrong and what I can do to solve the problem? Thanks in advance.</p>
  
  <p>EDIT:
  As Mariusz asks, here there is the error I get by add %tb at the beginning of the cell:</p>
  
  <pre><code>SystemExit                                Traceback (most recent call last)
  &lt;ipython-input-4-5757c6364c65&gt; in &lt;module&gt;()
        8     return '&lt;h1&gt;Hello World!&lt;/h1&gt;'
        9 if __name__ == '__main__':
  ---&gt; 10     app.run(debug=True)
  
  C:\Users\Antonio\Anaconda3\lib\site-packages\flask\app.py in run(self, host, port, debug, **options)
      841         options.setdefault('passthrough_errors', True)
      842         try:
  --&gt; 843             run_simple(host, port, self, **options)
      844         finally:
      845             # reset the first request information if the development server
  
  C:\Users\Antonio\Anaconda3\lib\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)
      690         from ._reloader import run_with_reloader
      691         run_with_reloader(inner, extra_files, reloader_interval,
  --&gt; 692                           reloader_type)
      693     else:
      694         inner()
  
  C:\Users\Antonio\Anaconda3\lib\site-packages\werkzeug\_reloader.py in run_with_reloader(main_func, extra_files, interval, reloader_type)
      248             reloader.run()
      249         else:
  --&gt; 250             sys.exit(reloader.restart_with_reloader())
      251     except KeyboardInterrupt:
      252         pass
  
  SystemExit: 1
  </code></pre>