Ah. See this comment, and the thread in general then → Multiselect jupyter notebook update value? - #6 by gmerritt123
“my current understanding is that output_notebook() will embed standalone html/JS and no longer “talk” to the python variables (so in your case input_widget, as an instance of a python class, its value property never gets altered, but its javascript equivalent does)… i.e. there’s no interaction between the python in your notebook and the html embedded in it.”