ipywidgets button on_click event not getting called in Jupyter Notebook / JupyterLab 7.X

[jsid72]

Description

ipywidgets works well in Jupyter Notebook 6.X but does not work in the latest Jupyter Notebook / JupyterLab 7.X.

Reproduce

1. Setup a new Python Virtual Environment with the latest Jupyter Notebook 7.X and ipywidgets 8.1.5
2. In a Jupyter Notebook run the following code:

from ipywidgets import widgets
from IPython.display import display
 
def test_function(btn):
    print("Button was clicked")
 
button = widgets.Button(description="Test Button")
button.on_click(test_function)
 
display(button)

3. Running the above code shows the button but clicking the button does not produce expected output.

The above code works as expected on running it in Jupyter Notebook 6.X

Expected behavior

Click on button should display output but nothing appears.

Context

• ipywidgets version 8.1.5
• Operating System and version: Windows 11
• Browser and version: Chrome 128

[rsnell-usgs]

@jsid72 You need to send the output to an Output widget as per this page: https://ipywidgets.readthedocs.io/en/latest/examples/Widget%20Events.html

from IPython.display import display
button = widgets.Button(description="Click Me!")
output = widgets.Output()

display(button, output)

def on_button_clicked(b):
    with output:
        print("Button clicked.")

button.on_click(on_button_clicked)

I was recently caught out by this same issue. In v6 of Notebook this output would be shown but not in v7 which is based on JupyterLab. JupyterLab sends output generated by events that are out of the normal processing flow to the log it would appear. A real pain and significant breaking change for sure. I was also caught out by the fact that VS Code behaves like Notebooks v6 and that si what I used to develop my Notebook, see here: microsoft/vscode-jupyter#15996