williamstein
commented
2 months ago This is a reasonable request given our current model of widgets, where all state is fully available in the backend (or compute server). We have full realtime sync between clients as well.
I think the way this would have to work would be the following:
- like with Jupyter, there is a menu item to persist the state of all widgets to disk. This would create a big json file on disk next to the notebook.
- a widget relies on python code being run to create data structures in memory of the python interpreter, so no matter what you have to run the code to create the widget. However, right after the widget is initialized, it would have its state set to the state that was saved on disk, and appropriate comm messages would be sent to the kernel (and browsers) so that they all have this state.
That's it. It's technically possible to do.
Presumably there is also a way to do this entirely using widgets too, e.g., a decorator that persists state to disk and loads it, somehow. That would be cool since it would be totally generic and work in jupyterlab, colab, etc. I bet somebody has written something like that...
It appears that ipywidgets are not persistent in cocalc. That is, if you make one like:
you can select a value, but if you close the project and restart it, the widget is gone.
If you just close and halt a notebook, then reopen it, the widgets appear to still be there. They seem to disappear when the project is closed.
Note in Jupyter Notebooks you have to manually Save the widget state from a menu. This does lead to a partial rendering of the widget, but it does not rebuild any connections, e.g. if you have an observe function on a widget that changes an output widget.
I don't know if there is something equivalent in Jupyter Lab.