Jupyter lab failing to launch

Question

I updated my conda environment today. Before, I could launch jupyter lab from the terminal. After the updates (which included installing theano, but I'm guessing that's unrelated), I get the following error that I do not understand:

marcel@flaptop:~$ jupyter lab
Traceback (most recent call last):
File "/home/marcel/anaconda3/bin/jupyter-lab", line 7, in <module> from jupyterlab.labapp import main
File "/home/marcel/anaconda3/lib/python3.6/site-packages/jupyterlab/labapp.py", line 7, in <module> from notebook.notebookapp import NotebookApp, aliases, flags  
File "/home/marcel/anaconda3/lib/python3.6/site-packages/notebook/notebookapp.py", line 45, in <module> ioloop.install()
File "/home/marcel/anaconda3/lib/python3.6/site-packages/zmq/eventloop/ioloop.py", line 210, in install assert (not ioloop.IOLoop.initialized()) or  AttributeError: type object 'IOLoop' has no attribute 'initialized'

Does anyone know what is going on here?t

Answer 1

Seems to be Tornado version 5. There's discussion here: Install Jupyter Notebook on Miniconda

pip uninstall tornado pip install tornado==4.5.3

fixed it for me, as posted in the link above.