Comms not cleared after re-executing cell with ipywidgets

[bd-Kwasniewski]

When I re-execute a cell that creates an ipywidget (e.g., IntSlider), the old comm is not closed and remains in get_ipython().kernel.comm_manager.comms. This leads to multiple comms accumulating after repeated executions, even after clearing the cell output.

Reproduce

1. execute in cell

import ipywidgets as widgets
from IPython.display import display

slider = widgets.IntSlider()
display(slider)

2. execute in second cell

get_ipython().kernel.comm_manager.comms

3. observe 3 comms present

4. rexecute cell 1

5. observe in cell 2 that 6 comms are present

Expected behavior

Old comms should be closed when the cell output is cleared or replaced, so only one comm remains per widget.

Context

• ipywidgets version 8.1.7
• Operating System and version: macos 15.5
• Browser and version: chrome 138.0.7204.169

[fleming79]

There is a PR open that addresses your issue here: #3921.

For automatic cleanup in the PR you'd still need to call.

widgets.enable_weakreference()

Or you could close the widget manually when you are done with it.

Note also there are 3x comm associated with that widget

1. slider widget
2. slider.layout (a widget)
3. slider.style (a widget)

slider.close()
slider.layout.close()
slider.style.close()