try to save, e.g. press Cmd+S

this

On Stack Overflow, a person named Scott astutely pointed out that the % seemed to be the issue. I was using it as the modulo operator. A workaround is to use operator.mod() instead. Still, I think this counts as a bug right?
Let me know if you need more info!
That does count as a bug! Though I'm not sure exactly whose bug it is.
From the answers on SO, it only seems to affect Chrome with the Lastpass extension installed. Is that the case for you too? I use Lastpass in Firefox, and I don't see the issue.
As a matter of fact, I do. So strange! No idea how I'd proceed from here though. Huh... talk about a corner case.
I know Lastpass does things with the page to find password fields to autofill, but I don't know why it would affect saving.
Here's a thread on the Lastpass forums about it. It sounds like it might also affect Google chat:
https://forums.lastpass.com/viewtopic.php?f=12&t=236645&p=791705&hilit=jupyter#p791705
Thanks again @takluyver . I've put in a ticket with LastPass support. I subscribe to their premium service. Let's see what it gets me. I'll update when I know more.
Yep getting the same. You can see the offending line of the plugin below:
"URIError: URI malformed
at decodeURI (<anonymous>)
at XMLHttpRequest.send (chrome-extension://hdokiejnpimakedhajhdlcegeplioahd/xhrExtension.js:2:51)
at Object.send (http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:89:9344)
at Function.ajax (http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:89:4804)
at http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:12787:15
at Object.promising_ajax (http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:12779:16)
at Contents.save (http://localhost:8888/static/services/contents.js?v=20161216120736:176:22)
at _save (http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:27436:34)
at http://localhost:8888/static/notebook/js/main.min.js?v=e80a0ad9bee7ad0d5865624902d5405d:27475:32"
I managed to disable the hook in, by adding "localhost" to My Vault -> Account Settings -> Neverl URLS -> "Never Add Site"
Seemed to prefer having it as a domain without any port or path.
Thank you @devgrok for the workaround! Edit: It works for me! I followed your instructions:
adding "localhost" to My Vault -> Account Settings -> Neverl URLS -> "Never Add Site"
In the meantime, I also got a response from LastPass, and they don't have a timeline for a fix so the best we can hope for is that they resolve it on their next release. Here is the link to the release update page: https://lastpass.com/upgrade.php?fromwebsite=1&releasenotes=1
I hope the next update comes out soon, this is super annoying as I have to disable LastPass just to use many websites normally.
If this is still affecting people, you may be able to use Firefox to work around it - Lastpass on Firefox does not have the issue.
Most helpful comment
Yep getting the same. You can see the offending line of the plugin below:
I managed to disable the hook in, by adding "localhost" to My Vault -> Account Settings -> Neverl URLS -> "Never Add Site"
Seemed to prefer having it as a domain without any port or path.