"Show cronjobs" displays error schedule

[suevii]

Hi,

Environment

Jupyterlab version: 3.0.6

Description

I found this issue when I click the "Show cronjobs" button.

Reproduce steps

The issue is randomly occured, to reproduce it:

1. add several jobs
2. delete some of them

Workaround

I found it was caused by the missing of blank line between the job and the previous variables in the system crontab file:

If I try to add a blank line, the issue is fixed.

I think there may be some bug when calling the /delete api (which delete some extra blank lines) or the regex pattern matching the schedule (but when I test the pattern outside the jupyterlab, it seems correct).
My current solution is to change the regex pattern matching the schedule in the get /list API:
schedule_match = re.search(r"(((\d+,)+\d+|(\d+(\/|-)\d+)|\d+|\*) ?){5,7}", str(job))
schedule = schedule_match.group(0)
instead of above code:
schedule = str(job.slices)

With this fix the issue is gone, but I'm not sure it causes other issue.
Please comment if anything wrong, thank you.😊

[jovanni-hernandez]

Thanks for reporting this bug and doing some digging to find the root cause - I'll try to get this implemented soon. I also ran into a new bug recently where that regexp doesn't work when the OS reinterprets the CRON strings as @daily @Weekly, etc, so it needs some tweaks.