[FIXED] ipywidgets.VBox not showing once part of function

Issue

I try to create an interactive dashboard using ipywidgets. (ipywidgets version 7.5.0, python version 3.7.2)

In a single batch of code, the widgets.VBox() shows automatically. But once I outsource the statement to a function, the widgets.VBox() does not show unless I explicitly wrap it in a display() statement. Here is a simple piece of code that works. It shows the slider on top and the number chosen times 5 at the bottom.

import ipywidgets as widgets
from IPython.display import display

def fa(a,b):
    display(a*b)

a = widgets.IntSlider(10)
out = widgets.interactive_output(fa,{'a':a,'b':widgets.fixed(5)})
widgets.VBox([a,out])

Once I put the VBox into an output function, nothing is displayed, not even an error message:

def fa(a,b):
    display(a*b)

def db(a,b):
   widgets.VBox([a,b])

a = widgets.IntSlider(10)
out = widgets.interactive_output(fa,{'a':a,'b':widgets.fixed(5)})
db(a,out)

But once I replace widgets.VBox([a,b]) in the db() function with display(widgets.VBox([a,b])) everything is back to normal.

Sorry, may be a basic question, but what is the system behind this behaviour?

Solution

If you're working in Notebook, the default behaviour is to print/display the last line of any cell to the output space below. Hence your widgets.VBox([a,out]) on the last line of your first snippet is actually display(widgets.VBox([a,out])) in disguise.

Answered By - ac24