Exceptions raised in DynamicMap callable not caught by exception handler

[TheoMathurin]

ALL software version info

Software Version Info

panel 1.9.3
holoviews 1.23.1
bokeh 3.9.1

Description of expected behavior and the observed behavior

I would have thought errors occurring in a DynamicMap callable would be handled by the exception handler. Instead, the handler function is not executed.

Complete, minimal, self-contained example code that reproduces the issue

In the following, a DynamicMap callable raises an exception for a particular value of the input. This exception is not handled. As a control I also include a button associated with a callback triggering an exception which is adequately handled.

import holoviews as hv
import numpy as np
import panel as pn


def exception_handler(e):
    """Handle and log unexpected exception and notifies user"""
    print(f"Unexpected Exception: {e}")
    pn.state.notifications.error(f"Unexpected Exception: {e}")


pn.extension(exception_handler=exception_handler, notifications=True)
pn.state.notifications.position = "top-left"


def raise_error(_):
    raise ValueError("Error raised")


def get_plot(value):
    if value == 4:
        raise ValueError("Error in plot")
    return hv.Points(data).opts(size=value)


data = np.random.rand(10, 2)
slider = pn.widgets.IntSlider(start=1, end=5, value=1)
dmap = hv.DynamicMap(pn.bind(get_plot, value=slider))
button = pn.widgets.Button(label="Button", on_click=raise_error)


pn.Column(button, dmap, slider).servable()

Stack traceback and/or browser JavaScript console output

2026-07-13 14:31:20,177 Starting Bokeh server version 3.9.1 (running on Tornado 6.5.7)
2026-07-13 14:31:20,177 User authentication hooks NOT provided (default user enabled)
2026-07-13 14:31:20,179 Bokeh app running at: http://localhost:5006/toast
2026-07-13 14:31:20,179 Starting Bokeh server with process id: 46581
2026-07-13 14:31:22,679 WebSocket connection opened
2026-07-13 14:31:22,680 ServerConnection created
Unexpected Exception: Error raised
WARNING:param.wrapped_sync: Callable raised "ValueError('Error in plot')".
Invoked as wrapped_sync(value=4)
2026-07-13 14:31:36,271 Callable raised "ValueError('Error in plot')".
Invoked as wrapped_sync(value=4)
Traceback (most recent call last):
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/holoviews/plotting/util.py", line 319, in get_plot_frame
    return map_obj[key]
           ~~~~~~~^^^^^
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/holoviews/core/spaces.py", line 1368, in __getitem__
    val = self._execute_callback(*tuple_key)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/holoviews/core/spaces.py", line 1118, in _execute_callback
    retval = self.callback(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/holoviews/core/spaces.py", line 675, in __call__
    ret = self.callable(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/param/depends.py", line 125, in _depends_sync
    return func(*args, **kw)
           ^^^^^^^^^^^^^^^^^
  File "/home/user/.cache/uv/archive-v0/cSuNtOvSrdXgSCur/lib/python3.12/site-packages/param/reactive.py", line 1353, in wrapped_sync
    return eval_fn()(*combined_args, **combined_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/project/test.py", line 22, in get_plot
    raise ValueError("Error in plot")
ValueError: Error in plot

Screenshots or screencasts of the bug in action

Capture.video.du.2026-07-13.14-31-27.webm