Button.on_click() handler is called twice for a single click

[decitre]

Description

Even in a minimal setup, a single click on an ipywidgets.Button causes the registered on_click handler to be called twice.

Reproduce

This occurs using JupyterLab 4.4.5 with ipywidgets 8.1.7 with the code snippet below.

import ipywidgets as widgets

def handler(*args, **kwargs):
    print(f"handler called with: args={args}, kvargs={kwargs}")

button = widgets.Button(description="Click me")
button.on_click(handler)

button

Output when clicking once:

handler called with: args=(Button(description='Click me', style=ButtonStyle()),), kvargs={}
handler called with: args=(Button(description='Click me', style=ButtonStyle()),), kvargs={}

Expected behavior

A single handler call per click

Context

• ipywidgets version 8.1.7
• Operating System and version: macOS 14.7.6 (23H626)
• Browser and version: Firefox 140.0.4 (aarch64)

Troubleshoot Output

python -m jupyter troubleshoot > jupyter-troubleshoot.txt

Command Line Output

python -m jupyterlab --debug > jupyterlab-debug.txt 2>&1

Browser Output

(See attached browser-javascript-console-pasted-content.txt)

If using JupyterLab

• JupyterLab version: 4.4.5

Installed Labextensions

python -m jupyter labextension list
JupyterLab v4.4.5
/Users/decitre/virtualenv/here-search-demo/share/jupyter/labextensions
        jupyterlab_pygments v0.3.0 enabled OK (python, jupyterlab_pygments)
        @jupyter-widgets/jupyterlab-manager v5.0.15 enabled OK (python, jupyterlab_widgets)

jupyter-troubleshoot.txt
browser-javascript-console-pasted-content.txt
jupyterlab-debug.txt

[maartenbreddels]

I'm wondering if it's not the printing that is double, did you double check by increasing a counter and printing that out?