Stacked widget dont work

On latest version this code produces error in chrome console.

import ipywidgets
ipywidgets.Stacked()

Error: Cannot find model module @jupyter-widgets/controls@1.5.0, StackedModel

Tried regenerate model schema (generate-spec.py) with no result.

[blois]

Colab’s in-progress support for 3rd party widgets builds off of the ipywidgets 8.0 alpha so it can be used- an example is: https://colab.research.google.com/gist/blois/2eed369f917b6e71a717684a65a06a84/stacked_widget.ipynb

I’m seeing an error when the selected_index is not specified for widgets.Stacked. I believe it comes from null being allowed here: https://github.com/jupyter-widgets/ipywidgets/blob/51cb73a0b31ed3f087de52d5122e565aa47b45f6/ipywidgets/widgets/widget_selectioncontainer.py#L19

But then that doesn’t appear to be handled here: https://github.com/jupyter-widgets/ipywidgets/blob/51cb73a0b31ed3f087de52d5122e565aa47b45f6/packages/controls/src/widget_selectioncontainer.ts#L442-L445

(But this error may be Colab-specific) (edit: specifying selected_index does appear to fix the issue in the binder link as well)

[shadiakiki1986]

@YoraiLevi ipywidgets.Stacked not working in colab is another issue: https://github.com/googlecolab/colabtools/issues/498#issuecomment-956321234