IPyleaflet does not consistently work with Panel

[2320sharon]

IPyleaflet does not consistently work with Panel

Description of expected behavior and the observed behavior

I've been attempting to create a Panel application with an ipyleaflet map in it. I have had issues getting the map to display using the command panel serve sample_app.py --show because it keeps displaying the same error message AttributeError: 'Map' object has no attribute 'widgets' even though I have installed all the relevant packages.

What's strange is that when I install the same packages in a different order is I get no errors . I have included three package_list.txt that show the two environments I created that showcase this strange behavior. In the working version of the environment I describe below I installed ipywidgets_bokeh first and then install panel and ipyleafelt whereas with the broken version of the environment I installed panel ipyleaflet first followed by ipywidgets_bokeh and it displayed the error message AttributeError: 'Map' object has no attribute 'widgets'.

Any idea why the order the packages being installed would impact whether this error message appears or not. I see each environment contains different versions of each package which may mean one package isn't compatible.
Thank you for any explanations for why this error might have occurred.

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

Working Version of Environment

I have included the versions of all the installed packages below in test_panel_package_list.txt, which ran successfully.

conda create -n test_panel
conda activate test_panel
conda install -c bokeh ipywidgets_bokeh -y
conda install -c conda-forge panel ipyleaflet -y
conda install -c conda-forge jupyterlab -y
panel serve sample_app.py --show

Broken Version of Environment

I have included the versions of all the installed packages below in test_panel2_package_list.txt, which displayed the error message below.

conda create -n test_panel2
conda activate test_panel2
conda install -c conda-forge panel ipyleaflet -y
conda install -c bokeh ipywidgets_bokeh -y
conda install -c conda-forge jupyterlab -y
panel serve sample_app.py --show

Sample Code

from ipyleaflet import Map, Marker

import panel as pn

pn.extension("ipywidgets", sizing_mode="stretch_width")

from ipyleaflet import Map, Marker

ACCENT_BASE_COLOR = "#DAA520"


def get_marker_and_map():
    center = (52.204793, 360.121558)

    lmap = Map(center=center, zoom=15, height=500)

    marker = Marker(location=center, draggable=True)
    lmap.add_layer(marker)
    lmap.layout.height="100%"
    lmap.layout.width="100%"
    return marker, lmap

marker, lmap = get_marker_and_map()

json_widget = pn.pane.JSON({}, height=75)

def on_location_changed(event):
    new = event["new"]
    json_widget.object = {"x": new[0], "y": new[1]}
marker.observe(on_location_changed, 'location')

component = pn.Column(
    pn.panel(lmap, sizing_mode="stretch_both", min_height=500),
    json_widget
)

template = pn.template.FastListTemplate(
    site="Awesome Panel",
    title="IPyLeaflet",
    logo="https://panel.holoviz.org/_static/logo_stacked.png",
    header_background=ACCENT_BASE_COLOR,
    accent_base_color=ACCENT_BASE_COLOR,
    main=[component],
).servable()

Stack traceback and/or browser JavaScript console output

(test_panel2) C:\1_USGS_repos\2_doodleverse\4_coastseg_panel\test2\panel-master\panel-master>panel serve sample_app.py --show
2022-08-24 09:38:10,477 Starting Bokeh server version 2.4.3 (running on Tornado 6.2)
2022-08-24 09:38:10,477 User authentication hooks NOT provided (default user enabled)
2022-08-24 09:38:10,482 Bokeh app running at: http://localhost:5006/sample_app
2022-08-24 09:38:10,482 Starting Bokeh server with process id: 22872
2022-08-24 09:38:11,483 Error running application handler <bokeh.application.handlers.script.ScriptHandler object at 0x000001B0DD567670>: 'Map' object has no attribute 'widgets'
File 'ipywidget.py', line 49, in _get_ipywidget:
for w in obj.widgets.values(): Traceback (most recent call last):
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\bokeh\application\handlers\code_runner.py", line 231, in run
    exec(self._code, module.__dict__)
  File "C:\1_USGS_repos\2_doodleverse\4_coastseg_panel\test2\panel-master\panel-master\sample_app.py", line 44, in <module>
    ).servable()
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\viewable.py", line 374, in servable
    self.server_doc(title=title, location=location) # type: ignore
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\template\base.py", line 332, in server_doc
    return self._init_doc(doc, title=title, location=location)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\template\base.py", line 553, in _init_doc
    doc = super()._init_doc(doc, comm, title, notebook, location)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\template\base.py", line 188, in _init_doc
    model = obj.get_root(doc, comm, preprocess=False)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\viewable.py", line 558, in get_root
    root = self._get_model(doc, comm=comm)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\layout\base.py", line 146, in _get_model
    objects = self._get_objects(model, [], doc, root, comm)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\layout\base.py", line 131, in _get_objects
    child = pane._get_model(doc, root, model, comm)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\pane\ipywidget.py", line 60, in _get_model
    model = self._get_ipywidget(self.object, doc, root, comm, **kwargs)
  File "C:\Users\sfitzpatrick\Anaconda3\envs\test_panel2\lib\site-packages\panel\pane\ipywidget.py", line 49, in _get_ipywidget
    for w in obj.widgets.values():
AttributeError: 'Map' object has no attribute 'widgets'

2022-08-24 09:38:11,700 WebSocket connection opened
2022-08-24 09:38:11,702 ServerConnection created
2022-08-24 09:38:53,075 WebSocket connection closed: code=1001, reason=Non

ALL software version info

OS: Windows 10
Anaconda Version: conda 4.10.3

Package List Files for Both Environments

1. Working Version
   test_panel_package_list.txt
2. Broken Version
   test_panel2_package_list.txt

[hoxbro]

I see the same error as you. If I downgrade ipywidgets with conda install "ipywidgets<8", I go from a broken environment to a working one.

[2320sharon]

Ah, so the issue might be with ipywidgets. Thanks for the tip about installing an older version of ipywidgets!

[hoxbro]

It seems like the new release of ipywidgets (released a week ago) moved widgets to _active_widgets, which is why the AttributeError occurs.

If that is the only change needed, the issue can be fixed by panel with an if statement.

[2320sharon]

I hope that's not too difficult of a fix. Do you mind showing what you think this if statement might look like?
Thanks for the tip about the ipywidget update to 8.0 apparently it changed quite a lot.

[hoxbro]

I would check the ipywidgets version with packaging.version and based on the version set the correct attribute here:

panel/panel/pane/ipywidget.py

Line 62 in be3c59a

for w in obj.widgets.values():

If you are up for it, you can make the PR.

[2320sharon]

Thank you for fixing this!