Clearly document requirement for pyviz_comms in JupyterLab environment

[MatusGasparik]

ALL software version info

• panel: 1.3.4
• param: 2.0.1
• jupyterlab: 4.0.8
• python: 3.11.6
• Browser: Chrome 119.0.6045.199 (arm64)

Description of expected behavior and the observed behavior

Creating UI widgets from param.Parametrized instances with parameter dependencies declared with the param.depends does NOT work - i.e. changing the params in the UI has no effect.

I'm genuinely puzzled by what I'm missing...

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

Example from the docs ()

import param
import panel as pn

print('param:', param.__version__)
print('panel:', pn.__version__)

pn.extension()


class Mul(param.Parameterized):
    a = param.Number(5,  bounds=(-100, 100))
    b = param.Number(-2, bounds=(-100, 100))

    @param.depends('a', 'b')
    def view(self):
        return str(self.a*self.b)

    def view2(self):
        return str(self.a*self.b)

prod = Mul(name='Multiplier')
pn.Row(prod.param, prod.view)

Stack traceback and/or browser JavaScript console output

• no errors

Screenshots or screencasts of the bug in action

Bildschirmaufnahme.2023-12-01.um.11.04.58.mov

[hoxbro]

Your example code works for me. What is your version of jupyterlab and pyviz_comms?

[MatusGasparik]

Thanks, @hoxbro for the very quick response. The JuperLab is v4.0.8.

Running jupter labexternsion list show no pyviz_comms... Am I missing the extension? I am going through the docs to see if I missed sth...

[hoxbro]

pyviz_comms is a python package

[MatusGasparik]

Thanks, that fixed the issue. I missed this step (but also couldn't find any mention in the panel docs...)

[hoxbro]

I'm not completely sure what is needed as pyviz_comms is a required dependency of panel.

[philippjfr]

If you install JupyterLab in a separate env from the kernel that panel is installed in then you need to make sure that pyviz_comms is explicitly installed.