key_press_event not working with matplotlib 3.10

[peter-urban]

Describe the issue

fig.canvas.mpl_connect('key_press_event', ...) does not work anymore with matplotlib 3.10. I compiled the following example to demonstrate this (run in a jupyter notebook):

%matplotlib widget
import matplotlib.pyplot as plt
import matplotlib

from ipywidgets import Output
from IPython.display import display

plt.close('test')
fig,ax = plt.subplots(num='test')

output = Output()
def event_handler(event):
    with output:
        print(event)

fig.canvas.mpl_connect('key_press_event', event_handler)
fig.canvas.mpl_connect('button_release_event', event_handler)

display(output)

When using matplotlib 3.9 the key press event and the mouse button release event cause the event_handler to print the event to the output. After upgrading to matplotlib 3.10, the button_release_event continues to work, but the key_press event does not produce any output anymore. When changing the matplotlib backend to qt (linemagic: "%matplotlib qt") the events work both for matplotlib 3.9 and 3.10

Versions

 3.12.8 | packaged by conda-forge | (main, Dec  5 2024, 14:24:40) [GCC 13.3.0]
ipympl version: 0.9.5
Selected Jupyter core packages...
IPython          : 8.30.0
ipykernel        : 6.29.5
ipywidgets       : 8.1.5
jupyter_client   : 8.6.3
jupyter_core     : 5.7.2
jupyter_server   : 2.14.2
jupyterlab       : 4.3.4
nbclient         : 0.6.8
nbconvert        : 7.16.4
nbformat         : 5.10.4
notebook         : not installed
qtconsole        : not installed
traitlets        : 5.14.3
Known nbextensions:
  config dir: /etc/jupyter/nbconfig
    notebook section
      jupyter-js-widgets/extension  enabled 
      - Validating: problems found:
        - require?  X jupyter-js-widgets/extension
JupyterLab v4.3.4
/ssd/opt/miniforge3/envs/dev/share/jupyter/labextensions
        jupyter-matplotlib v0.11.5 enabled OK
        jupyterlab_pygments v0.3.0 enabled OK (python, jupyterlab_pygments)
        jupyter-leaflet v0.19.2 enabled OK
        jupyterlab-execute-time v3.2.0 enabled OK (python, jupyterlab_execute_time)
        @jupyter-widgets/jupyterlab-manager v5.0.13 enabled OK (python, jupyterlab_widgets)

[ianthomas23]

Thanks for the bug report. This is caused by the line

ipympl/ipympl/backend_nbagg.py

Line 387 in efd2e5c

if matplotlib.__version__ < '3.4':

which does a string comparison of the matplotlib version so '3.10.0' is incorrectly identified as being earlier than '3.4'. The line should instead be

    if matplotlib.__version_info__ < (3, 4):

I'll fix this and do a new release as this is obviously a significant bug.