holoviews: No such comm: hv-extension-comm error in cmd prompt

The message ‘[IPKernelApp] WARNING | No such comm: hv-extension-comm’ has started appearing in my cmd prompt when trying to run a certain Jupyter notebook. However, it does not cause errors to appear in my browser console, and it does not stop the panel-based pipeline in the notebook from running correctly through all stages when prompted.

During the running of the same Jupyter notebook, I have started experiencing issues with visualizations using geoviews, so that images of shapefiles that previously appeared normally with the same code now appear blurry, are distorted, and show weird coloration. Therefore, I am making an initial assumption that the issue is related to the hv-extension-comm message that has started appearing in my cmd prompt.

The code that I am using to visualize is as follows near the end of a function:

shape_viz_p1 = gv.Shape.from_shapefile(self.file_param) shape_viz_p2 = datashade(shape_viz_p1, cmap=["blue"], precompute=True)* gvts.EsriImagery return pn.panel(shape_viz_p1)

The file path is valid (and I have tried using multiple shape files). The problem with the image being distorted occurs even in another notebook I am using that was previously producing a “normal” image. Also, the problem occurs regardless of whether or not I impose the overlay with EsriImagery.

No error message is produced in a traceback; the only indications of an issue are the message in the cmd prompt and the distorted image.

Please advise if you need any more info to assist. Thanks!

About this issue

Original URL
State: closed
Created 5 years ago
Comments: 24 (9 by maintainers)

Most upvoted comments

I see that the issue was previously mentioned in the now-closed issue of https://github.com/pyviz/holoviews/issues/3617, but no information is provided about what was done to resolve the issue there beyond the “solution” of placing code into another notebook.

WilliamBLeonard on Jul 5, 2019

Open a PR to fix it and earn $500 🙂

jbednar on Jun 20, 2021

I had the same problem and it was solved installing holoviews again. See: https://holoviews.org/user_guide/Installing_and_Configuring.html

cpalacios1965 on Feb 6, 2021

Nope; still open and ready to be claimed!

jbednar on Jan 20, 2022

I personally would pay $500 USD to anyone who can make these messages go away safely (i.e. without obscuring other messages that do actually mean something). Any takers?

I can reproduce this warning with the following procedure:

Import holoviews and create a plot, e.g.

import holoviews as hv
import numpy as np
hv.extension('bokeh')

N = 100
x = np.random.normal(size=N)
y = np.random.normal(size=N)

hv.Points((x, y))

Restart the kernel and execute the cell again. EDIT: if you restart and clear outputs, the error shows up immediately.

The error doesn’t show up the first time, and it doesn’t show up if the hv.extension('bokeh') statement is in a different cell from the plot. I imagine this is why it’s so commonly seen in issues, since it will appear most often when trying to debug something with a short example.

Inspecting the error, it is indeed calling CommManager.comm_open() before hv-extension-comm has been registered as a target (it gets registered after).

This seems like perhaps different JS components are in a race with each other? Although it’s very consistent so the race is pretty one-sided.

jamestwebber on Jun 20, 2021

Just to be sure it’s clear, this Github issue is about bogus messages that you see saying “No such comm target registered: hv-extension-comm” or “No such comm: hv-extension-comm”. The messages are themselves the actual issue, not a symptom of some other problem, because the messages are alarming while not indicating any actual error. Users often post these messages when they encounter a real problem, in the hopes that the messages will help debug that problem, but really those messages are a “red herring” that is unrelated to whatever problem is happening for that user. So any “solution” in any of the issues linked here is not a solution to this issue, i.e. that the messages are printed at all, which remains unsolved.

I personally would pay $500 USD to anyone who can make these messages go away safely (i.e. without obscuring other messages that do actually mean something). Any takers?

jbednar on Dec 18, 2020