[Bug]: button event key error when using %matplotlib widget in jupyter lab #29578

Bug summary

Python 3.11
import ipympl
import ipywidgets
import matplotlib
print("ipympl:", ipympl.version)
print("ipywidgets:", ipywidgets.version)
print("matplotlib:", matplotlib.version)

ipympl: 0.9.3
ipywidgets: 8.1.5
matplotlib: 3.10.0

%matplotlib widget

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])

def on_click(event):
print("Click detected at", event.xdata, event.ydata)

fig.canvas.mpl_connect('button_press_event', on_click)
plt.show()

Code for reproduction

%matplotlib widget

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])

def on_click(event):
    print("Click detected at", event.xdata, event.ydata)

fig.canvas.mpl_connect('button_press_event', on_click)
plt.show()

Actual outcome

No printing when a click event occurred

In the info log: ---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/ipympl/backend_nbagg.py:279, in Canvas._handle_message(self, object, content, buffers)
276 self.manager.handle_json(content)
278 else:
--> 279 self.manager.handle_json(content)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:474, in FigureManagerWebAgg.handle_json(self, content)
473 def handle_json(self, content):
--> 474 self.canvas.handle_event(content)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:264, in FigureCanvasWebAggCore.handle_event(self, event)
261 e_type = event['type']
262 handler = getattr(self, f'handle_{e_type}',
263 self.handle_unknown_event)
--> 264 return handler(event)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:288, in FigureCanvasWebAggCore._handle_mouse(self, event)
286 e_type = event['type']
287 button = event['button'] + 1 # JS numbers off by 1 compared to mpl.
--> 288 buttons = { # JS ordering different compared to mpl.
289 button for button, mask in [
290 (MouseButton.LEFT, 1),
291 (MouseButton.RIGHT, 2),
292 (MouseButton.MIDDLE, 4),
293 (MouseButton.BACK, 8),
294 (MouseButton.FORWARD, 16),
295 ] if event['buttons'] & mask # State after press/release.
296 }
297 modifiers = event['modifiers']
298 guiEvent = event.get('guiEvent')

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:295, in (.0)
286 e_type = event['type']
287 button = event['button'] + 1 # JS numbers off by 1 compared to mpl.
288 buttons = { # JS ordering different compared to mpl.
289 button for button, mask in [
290 (MouseButton.LEFT, 1),
291 (MouseButton.RIGHT, 2),
292 (MouseButton.MIDDLE, 4),
293 (MouseButton.BACK, 8),
294 (MouseButton.FORWARD, 16),
--> 295 ] if event['buttons'] & mask # State after press/release.
296 }
297 modifiers = event['modifiers']
298 guiEvent = event.get('guiEvent')

KeyError: 'buttons'
12:05:24 PM

KeyError Traceback (most recent call last)
File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/ipympl/backend_nbagg.py:279, in Canvas._handle_message(self, object, content, buffers)
276 self.manager.handle_json(content)
278 else:
--> 279 self.manager.handle_json(content)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:474, in FigureManagerWebAgg.handle_json(self, content)
473 def handle_json(self, content):
--> 474 self.canvas.handle_event(content)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:264, in FigureCanvasWebAggCore.handle_event(self, event)
261 e_type = event['type']
262 handler = getattr(self, f'handle_{e_type}',
263 self.handle_unknown_event)
--> 264 return handler(event)

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:288, in FigureCanvasWebAggCore._handle_mouse(self, event)
286 e_type = event['type']
287 button = event['button'] + 1 # JS numbers off by 1 compared to mpl.
--> 288 buttons = { # JS ordering different compared to mpl.
289 button for button, mask in [
290 (MouseButton.LEFT, 1),
291 (MouseButton.RIGHT, 2),
292 (MouseButton.MIDDLE, 4),
293 (MouseButton.BACK, 8),
294 (MouseButton.FORWARD, 16),
295 ] if event['buttons'] & mask # State after press/release.
296 }
297 modifiers = event['modifiers']
298 guiEvent = event.get('guiEvent')

File ~/anaconda3/envs/catan_test/lib/python3.11/site-packages/matplotlib/backends/backend_webagg_core.py:295, in (.0)
286 e_type = event['type']
287 button = event['button'] + 1 # JS numbers off by 1 compared to mpl.
288 buttons = { # JS ordering different compared to mpl.
289 button for button, mask in [
290 (MouseButton.LEFT, 1),
291 (MouseButton.RIGHT, 2),
292 (MouseButton.MIDDLE, 4),
293 (MouseButton.BACK, 8),
294 (MouseButton.FORWARD, 16),
--> 295 ] if event['buttons'] & mask # State after press/release.
296 }
297 modifiers = event['modifiers']
298 guiEvent = event.get('guiEvent')

KeyError: 'buttons'
12:05:24 PM

Expected outcome

print("Click detected at", event.xdata, event.ydata). This should print out the click coordinates

Additional information

No response

Operating system

Mac 15.1.1 (24B91), M2

Matplotlib Version

matplotlib: 3.10.0

Matplotlib Backend

module://ipympl.backend_nbagg

Python version

Python 3.11.11

Jupyter version

4.3.4

Installation

conda