[FIXED] Cannot connect to Jupyter Notebook

Issue

My environment:

Windows 10 Professional Python 3.7.2 virtualenv 16.4.3

I created a new virtual environment with D:\Python37\Scripts\virualenv env

Then I activated the virtual environment with env\Scripts\activate

Then I installed jupyter with pip install --upgrade jupyter

Finally, I started jupyter with jupyter notebook

Everything starts up fine, and I create a new Python 3 notebook. Unfortunately, the notebook never connects to the server. I get the following error message in powershell

Replacing stale connection: (token)

In the browser, I get the following error message:

"A connection to the notebook server could not be established. The notebook will continue trying to reconnect. Check your network connection or notebook server configuration."

My two prior virtual environments (with Jupyter) work fine. I've deleted .ipython, .jupyter, AppData\Roaming\jupyter, without any luck.

I've cleared cookies from my browser and have tried a different browser. Nothing works.

I've created two other virtual environments before, and both of those still work.

All jupyter notebooks in the two working environments start up as untrusted, whereas the new environment starts up as trusted. I'm guessing that I clicked on something and now the notebook is looking to start up in a trusted fashion - which may require HTTPS.

Where do I look to fix this problem?

Solution

This appears to be a tornado issue. I found clues here.

1. Jupyter no connection to server
2. Jupyter kernel not connecting

I looked at the version of tornado (from the above links) in an environment that was working. It turns out that the version was 5.1.1.

I looked at the version of tornado in an environment that was NOT working. It turns out that the version was 6.0.

I downgraded the version of tornado in my non-working environment to 5.1.1 with the following command.

pip install --upgrade tornado==5.1.1

And now the non-working environment works!

Answered By - Mark Eggers