Jupyter Lab: Error displaying widget: model not found

[tecamenz]

Describe the issue

I'm using the Jupyter Lab widget to generate interactive plots. So fare, plotting works nicely. There is only one problem: If I save the notebook, close the kernel and reopen the notebook the next day, all plots are gone and I only see the message "Error displaying widget: model not found". Is this expected behavior?

Versions

ipympl version: 0.5.7
jupyter core     : 4.6.3
jupyter-notebook : 6.1.1
qtconsole        : not installed
ipython          : 7.17.0
ipykernel        : 5.3.4
jupyter client   : 6.1.6
jupyter lab      : 2.2.2
nbconvert        : 5.6.1
ipywidgets       : 7.5.1
nbformat         : 5.0.7
traitlets        : 4.3.3
Known nbextensions:
  config dir: C:\Users\Cam\miniconda3\envs\oposad\etc\jupyter\nbconfig
    notebook section
      jupyter-matplotlib/extension enabled
      - Validating: ok
      jupyter-js-widgets/extension enabled
      - Validating: ok
JupyterLab v2.2.2
Known labextensions:
   app dir: C:\Users\Cam\miniconda3\envs\oposad\share\jupyter\lab
        @jupyter-widgets/jupyterlab-manager v2.0.0 enabled  ok
        jupyter-matplotlib v0.7.3 enabled  ok

[zesty]

EDIT: you do have to run the cell again to re-render the plot 💯 There's a more helpful bit from the plain notebook (localhost:8888/tree) when cold restarting a kernel:

"A Jupyter widget could not be displayed because the widget state could not be found. This could happen if the kernel storing the widget is no longer available, or if the widget state was not saved in the notebook. You may be able to create the widget by running the appropriate cells."

jupyter lab will just give the "model not found" errors (one for the plot, one for the control) and not render the static plot (the plain notebook will render the static image and give the verbose control error)

I've been seeing similar flakiness. I had widgets working a couple days ago in stock defaults conda base env, then I touched it.

Just managed to get a conda env working by installing from that pure defaults base env with:

conda create --name forge
conda activate forge
conda install -c conda-forge jupyterlab ipympl
jupyter labextension install @jupyter-widgets/jupyterlab-manager
jupyter labextension install jupyter-matplotlib

working testcase:

%matplotlib widget
from ipywidgets import *
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 2*np.pi)
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
line, = ax.plot(x, np.sin(x))

def update(w = 1.0):
    line.set_ydata(np.sin(w * x))
    fig.canvas.draw_idle()

interact(update);

% jupyter nbextension list 
jupyter labextension list
Known nbextensions:
  config dir: /home/user/anaconda3/envs/forge/etc/jupyter/nbconfig
    notebook section
      jupyter-matplotlib/extension  enabled 
      - Validating: OK
      jupyter-js-widgets/extension  enabled 
      - Validating: OK
JupyterLab v2.2.4
Known labextensions:
   app dir: /home/user/anaconda3/envs/forge/share/jupyter/lab
        @jupyter-widgets/jupyterlab-manager v2.0.0  enabled  OK
        jupyter-matplotlib v0.7.3  enabled  OK

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[tecamenz]

EDIT: you do have to run the cell again to re-render the plot 💯 There's a more helpful bit from the plain notebook (localhost:8888/tree) when cold restarting a kernel:

"A Jupyter widget could not be displayed because the widget state could not be found. This could happen if the kernel storing the widget is no longer available, or if the widget state was not saved in the notebook. You may be able to create the widget by running the appropriate cells."

jupyter lab will just give the "model not found" errors (one for the plot, one for the control) and not render the static plot (the plain notebook will render the static image and give the verbose control error)

So this is expected behavior and no way the last state of the plots can be saved in the notebook? If so, I think this is an important feature to add don't you think?

[martinRenou]

Thanks. This is a known issue, closing as duplicate of #16.