title: Jupyter Notebook: 500 Internal Server Error
body: <p>I was trying to open a .ipynb file in Jupyter Notebook when I got a "500: Internal Server Error" in my browser.</p>
  
  <p>error message in the terminal:</p>
  
  <pre><code>[C 23:01:41.750 NotebookApp]
  
      To access the notebook, open this file in a browser:
          file:///C:/Users/Valeera/AppData/Roaming/jupyter/runtime/nbserver-6072-open.html
      Or copy and paste one of these URLs:
          http://localhost:8888/?token=c33d644eeb15c66ec4f8764c7e83023f729f162bbc122f38
  [E 23:01:44.821 NotebookApp] Uncaught exception GET /notebooks/1700012779.ipynb (::1)
      HTTPServerRequest(protocol='http', host='localhost:8888', method='GET', uri='/notebooks/1700012779.ipynb', version='HTTP/1.1', remote_ip='::1')
      Traceback (most recent call last):
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\tornado\web.py", line 1697, in _execute
          result = method(*self.path_args, **self.path_kwargs)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\tornado\web.py", line 3174, in wrapper
          return method(self, *args, **kwargs)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\notebook\handlers.py", line 59, in get
          get_custom_frontend_exporters=get_custom_frontend_exporters
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\base\handlers.py", line 462, in render_template
          return template.render(**ns)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\jinja2\asyncsupport.py", line 76, in render
          return original_render(self, *args, **kwargs)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\jinja2\environment.py", line 1008, in render
          return self.environment.handle_exception(exc_info, True)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\jinja2\environment.py", line 780, in handle_exception
          reraise(exc_type, exc_value, tb)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\jinja2\_compat.py", line 37, in reraise
          raise value.with_traceback(tb)
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\templates\notebook.html", line 1, in top-level template code
          {% extends "page.html" %}
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\templates\page.html", line 154, in top-level template code
          {% block header %}
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\templates\notebook.html", line 120, in block "header"
          {% for exporter in get_custom_frontend_exporters() %}
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\notebook\notebook\handlers.py", line 19, in get_custom_frontend_exporters
          from nbconvert.exporters.base import get_export_names, get_exporter
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\nbconvert\__init__.py", line 7, in &lt;module&gt;
          from . import postprocessors
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\nbconvert\postprocessors\__init__.py", line 5, in &lt;module&gt;
          from .serve import ServePostProcessor
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\nbconvert\postprocessors\serve.py", line 19, in &lt;module&gt;
          class ProxyHandler(web.RequestHandler):
        File "C:\Users\Valeera\Anaconda3\lib\site-packages\nbconvert\postprocessors\serve.py", line 21, in ProxyHandler
          @web.asynchronous
      AttributeError: module 'tornado.web' has no attribute 'asynchronous'
  [E 23:01:44.833 NotebookApp] {
        "Host": "localhost:8888",
        "Connection": "keep-alive",
        "Upgrade-Insecure-Requests": "1",
        "Dnt": "1",
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36",
        "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8",
        "Referer": "http://localhost:8888/tree",
        "Accept-Encoding": "gzip, deflate, br",
        "Accept-Language": "en-US,en;q=0.9,zh-CN;q=0.8,zh;q=0.7",
        "Cookie": "_xsrf=2|2008cea6|390d6f74fcb21ba19bd6f0383f3c2abd|1552660846; username-localhost-8888=\"2|1:0|10:1552662103|23:username-localhost-8888|44:YjUyZWQzMmVhYzYxNDY5NDk4ZGNkNDFhMzhhZWUyOWY=|048e17c293599d50a07b2f0a1cbcdaadbb04e21f8a3b167947e1caee099b442f\""
      }
  </code></pre>
  
  <p>It seems something went wrong with module <code>'tornado.web'</code>, which I totally have no idea about. Could someone tell me what to do to get my Jupyter Notebook work again?</p>