Remove In[*] from cells when notebook is restarted

[dpsanders]

I often restart a notebook when a cell hangs.
If several cells were executed, they are all left with In[*] when the notebook is restarted, which can be confusing.

I suggest simply removing all occurrences of In[*] when the notebook is restarted.

[takluyver]

That sounds reasonable to me, and should hopefully be easy to implement. I think you could just add a handler for the kernel_restarting.Kernel event.

[danagilliann]

Hey! Can I try to tackle this issue?

[takluyver]

Please do! Can you see what you might need to do? You'll probably want to search for the kernel_restarting.Kernel event in the Javascript code to see where it's fired and how other code uses it.

[danagilliann]

Sweet! I'll probably get to this on Friday

[danagilliann]

And I got to this much earlier than Friday. I'm looking into doing something here. Am I looking in the right place? If I am, does anyone have any suggestions on removing the In[*] instances?

[takluyver]

The code that updates the In [ ]: prompts is in codecell.js - search for set_input_prompt

[danagilliann]

I'm thinking of adding an if statement to determine if the notebook has been restarted somewhere here my only issue though is i'm not sure how to determine if the notebook had been restarted. I'm not sure if this is the way I should be going about this since i'm not sure if there is any data to tell me anything about that.

[takluyver]

That code runs when the user executes a cell - I think the issue here is with restarting the kernel after that has happened.

I think the way to do this will be to handle the kernel_restarting event in codecell.js , in the bind_events method - i.e. add some code like this:

notebook/notebook/static/notebook/js/notificationarea.js

Lines 117 to 120 in faa0cab

	this.events.on('kernel_restarting.Kernel', function () {
	that.save_widget.update_document_title();
	knw.set_message(i18n.msg._("Restarting kernel"), 2000);
	});

But inside the handler, if the prompt number is '*' set it back to nothing.

[danagilliann]

Hi! I'm making some progress on the issue. I was able to write the event listener here. The issue I'm having now is that it doesn't seem to actually run when the event is triggered since nothing is logging to the console. Am I doing something wrong?

[takluyver]

That looks right. Stick a console.log() above it to check that bind_events() is getting called for each code cell. 😕

[danagilliann]

Hmm doesn't seem to calling it. I even tried running the debugger 😢

[takluyver]

I just tried your branch, and when I restart the kernel, I do see KERNEL HAS RESTARTED in the Javascript console.

Are you rebuilding the Javascript after modifying it? The notebook doesn't load the separate js files directly - instead they're bundled into one big file to make it load quicker. There are instructions on how to work with this here: http://jupyter-notebook.readthedocs.io/en/stable/contributing.html#setting-up-a-development-environment

[danagilliann]

Hmm I did try that, but it's still not showing up for me. I even tried restarting the notebook. I'm just supposed to run jupyter notebook inside the repo for it to run in dev mode, right?

[takluyver]

It doesn't matter where you run the command, but you need to do pip install -e . to do a development install, and then run npm run build (or setup.py js css, which is equivalent) each time you change it to rebuild the Javascript.

You might also need to hard refresh your browser a couple of times to make sure it's not loading the JS from cache.
`

[danagilliann]

Argh. It's still not working and I also ran it in incognito mode :(

[takluyver]

Possibly you're not running the copy of the notebook package that you've modified. This can be fiddly. Try these steps:

• Uninstall all copies of the notebook package you can find
• Run python -m pip install -e . in the notebook repository to install from there
• Run npm run build to make sure the JS & CSS is up to date
• Check that it's finding the version of the notebook you meant with python -c "import notebook; print(notebook)" (check the path it shows)
• Launch with python -m notebook --port 8989 , and check that the browser is pointing to localhost:8989 (rather than the default 8888). This is just a random port that's not the default, there's nothing special about it.
• Go to Help -> About in the notebook menus and check that the version number for the notebook server is a development version:

[takluyver]

Closed by #3494