Fix missing return types
Fix missing return types

Signed-off-by: martinRenou <a8278cece597ec79cc59974d3d55dbb79bb38416@gmail.com>

ipython/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,jupyter-widgets/ipywidgets,jupyter-widgets/ipywidgets