Improvement: highlight updating cells in reactive mode

[stefaneidelloth]

If a cell takes a while to calculate it would be nice to highlight updating/stale cells.

Cells 1 and 3 should be marked while cell 2 is working:

Maybe with colors similar to nbsafety:
https://nbsafety.org/docs/#Running

Or with grey gutter line like in observablehq:
https://observablehq.com/d/797362a5c2538221

[davidbrochart]

Cells 1 and 3 should be marked while cell 2 is working

There might be a misunderstanding here. The reactive mode is not cell-based, meaning that the time.sleep in cell 2 doesn't matter because it's not part of a's assignment. b and c are only linked to a change in a's value. So if in another cell you have a = 100, b and c will update immediately (the sleep won't be executed again).
That being said, yes I think it could be possible to highlight a's dependencies (and sub-dependencies) whenever it is assigned to, until they are updated. Thanks for sharing the idea!

[davidbrochart]

Done in davidbrochart/ipyx#8. You can try it with pip install ipyx==0.1.4.