panel 1.4.3 regression: KeyError: 'content' in jupyterlab

[avivazran]

ALL software version info

OS: win10
Jupyter Lab Version 4.1.5
bokeh version: 3.4.1
Python version: 3.9.13

Description of expected behavior and the observed behavior

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

multi_select = pn.widgets.MultiSelect(name='MultiSelect', value=['Apple', 'Pear'],
    options=['Apple', 'Banana', 'Pear', 'Strawberry'], size=8)

multi_select

Traceback (most recent call last):
  File "C:\PythonCodes\SEVToolBox\sev_tools_env\sevtoolboxenv\lib\site-packages\pyviz_comms\__init__.py", line 340, in _handle_msg
    self._on_msg(msg)
  File "C:\PythonCodes\SEVToolBox\sev_tools_env\sevtoolboxenv\lib\site-packages\panel\viewable.py", line 469, in _on_msg
    patch = manager.assemble(msg)
  File "C:\PythonCodes\SEVToolBox\sev_tools_env\sevtoolboxenv\lib\site-packages\panel\models\comm_manager.py", line 29, in assemble
    msg_obj = cls(header, msg['metadata'], msg['content'])
KeyError: 'content'

Stack traceback and/or browser JavaScript console output

Screenshots or screencasts of the bug in action

• I may be interested in making a pull request to address this

[hoxbro]

Can't seem to recreate it. Can you check if you have the latest version of pyviz_comms?

[xdev-x]

Same issue here, with the latest version of pyviz_comms. How can we help you to reproduce ?

[avivazran]

Looks like issue affects widgets based on jupyter widgets or ipywidgets. Issue is gone after pulling previous environment from git. My venv code sits on its own repo.

[xdev-x]

@avivazran what are the package version you are using ?

On my side, I have the issue in a venv with

(jupyterlab + holoviews[recommended])

Package                   Version
------------------------- --------------
anyio                     4.4.0
appnope                   0.1.4
argon2-cffi               23.1.0
argon2-cffi-bindings      21.2.0
arrow                     1.3.0
asttokens                 2.4.1
async-lru                 2.0.4
attrs                     23.2.0
Babel                     2.15.0
beautifulsoup4            4.12.3
bleach                    6.1.0
bokeh                     3.4.1
certifi                   2024.2.2
cffi                      1.16.0
charset-normalizer        3.3.2
colorcet                  3.1.0
comm                      0.2.2
contourpy                 1.2.1
cycler                    0.12.1
debugpy                   1.8.1
decorator                 5.1.1
defusedxml                0.7.1
executing                 2.0.1
fastjsonschema            2.19.1
fonttools                 4.52.4
fqdn                      1.5.1
h11                       0.14.0
holoviews                 1.18.3
httpcore                  1.0.5
httpx                     0.27.0
idna                      3.7
ipykernel                 6.29.4
ipython                   8.24.0
isoduration               20.11.0
jedi                      0.19.1
Jinja2                    3.1.4
json5                     0.9.25
jsonpointer               2.4
jsonschema                4.22.0
jsonschema-specifications 2023.12.1
jupyter_client            8.6.2
jupyter_core              5.7.2
jupyter-events            0.10.0
jupyter-lsp               2.2.5
jupyter_server            2.14.0
jupyter_server_terminals  0.5.3
jupyterlab                4.2.1
jupyterlab_pygments       0.3.0
jupyterlab_server         2.27.2
kiwisolver                1.4.5
linkify-it-py             2.0.3
Markdown                  3.6
markdown-it-py            3.0.0
MarkupSafe                2.1.5
matplotlib                3.9.0
matplotlib-inline         0.1.7
mdit-py-plugins           0.4.1
mdurl                     0.1.2
mistune                   3.0.2
nbclient                  0.10.0
nbconvert                 7.16.4
nbformat                  5.10.4
nest-asyncio              1.6.0
notebook                  7.2.0
notebook_shim             0.2.4
numpy                     1.26.4
overrides                 7.7.0
packaging                 24.0
pandas                    2.2.2
pandocfilters             1.5.1
panel                     1.4.3
param                     2.1.0
parso                     0.8.4
pexpect                   4.9.0
pillow                    10.3.0
pip                       24.0
platformdirs              4.2.2
prometheus_client         0.20.0
prompt_toolkit            3.0.45
psutil                    5.9.8
ptyprocess                0.7.0
pure-eval                 0.2.2
pycparser                 2.22
Pygments                  2.18.0
pyparsing                 3.1.2
python-dateutil           2.9.0.post0
python-json-logger        2.0.7
pytz                      2024.1
pyviz_comms               3.0.2
PyYAML                    6.0.1
pyzmq                     26.0.3
referencing               0.35.1
requests                  2.32.2
rfc3339-validator         0.1.4
rfc3986-validator         0.1.1
rpds-py                   0.18.1
Send2Trash                1.8.3
six                       1.16.0
sniffio                   1.3.1
soupsieve                 2.5
stack-data                0.6.3
terminado                 0.18.1
tinycss2                  1.3.0
tornado                   6.4
tqdm                      4.66.4
traitlets                 5.14.3
types-python-dateutil     2.9.0.20240316
typing_extensions         4.12.0
tzdata                    2024.1
uc-micro-py               1.0.3
uri-template              1.3.0
urllib3                   2.2.1
wcwidth                   0.2.13
webcolors                 1.13
webencodings              0.5.1
websocket-client          1.8.0
xyzservices               2024.4.0

[ahuang11]

I think downgrading to 1.4.2 works pip install panel!=1.4.3. Just be sure to restart kernel / close browser / clear browser cache after.

If I had to guess, I think it might be related to #6818

[pmav99]

I think downgrading to 1.4.2 works pip install panel!=1.4.3. Just be sure to restart kernel / close browser / clear browser cache after.

@ahuang I think that the trick is to actually "clean" the notebook. (e.g. nbstripout or "Restart and clean all cell outputs"). If I understand this correctly, panel.extension() injects some JS code in the *.ipynb file which loads the JS/CSS files from the CDN. If you don't clean the notebook, then as soon as the browser page loads, this JS code seems to gets executed (even before executing any cells) and the result is that you get the behavior of the "before-the-update" panel version.

[pmav99]

Actually the trick is to:

1. Execute "Restart kernel and clear the outputs of All Cells"
2. Save the notebook: Ctrl + s
3. "Hard" reload the browser tab: usually Ctrl + F5 or Shift + Ctrl + F5 but it depends on the browser.

[vsriram11]

I'm facing the same issue, and the fix suggested above to restart/hard reload does not work for me. The regression is actually from 1.3.8 to 1.4.0, fixing panel version to 1.3.8 resolves the issue for me.

[pmav99]

Nope. 1.4.1 and 1.4.2 work fine. But you must clean the notebook and save it before you reload the tab and restart the kernel. That being said if you don't need some feature from panel 1.4 (or bokeh 3.4) then you are fine with downgrading to 1.3, too

[MarcSkovMadsen]

I also experienced this issue in our Jupyterlab after upgrading its Python environment.

[philippjfr]

Yes, this is an urgent regression. Will release 1.4.4 tomorrow.