# Catalyst connection freezes in Jupyter

**URL:** https://discourse.paraview.org/t/catalyst-connection-freezes-in-jupyter/17342
**Category:** In Situ Support
**Tags:** catalyst, python
**Created:** [December 2, 2025, 8:36pm UTC](https://discourse.paraview.org/t/catalyst-connection-freezes-in-jupyter/17342 "2025-12-02T20:36:41Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![greg](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/g/71c47a/32.png) [@greg](https://discourse.paraview.org/u/greg)
#### Post date: [December 2, 2025, 8:36pm UTC](https://discourse.paraview.org/t/catalyst-connection-freezes-in-jupyter/17342/1 "2025-12-02T20:36:41Z")

</div>

I am trying to connect from Jupyter to a catalyst in situ simulation, but Jupyter freezes in the moment, when the in situ side connects. ( The aim of this experiment is to show some statistics, no graphics, in Jupyter from the insitu side.)

What I did:

- Installed the iparaview kernel in Jupyter, works without problems
- Run a modified version of Examples/PythonClient/catalystLiveVisualizer.py in Jupyter
- Start ./CxxFullExample feslicescript.py as suggested in the above example
- at this moment, the \_monitorServerNotifications() loop stops

I attach my modified version of Examples/PythonClient/catalystLiveVisualizer.py with the following changes:

- all Rendering related calls removed
- \_monitorServerNotifications(), \_updateEventCb(), \_connectionCreatedEventCb() print a message

When I start the attached script in pvpython, it works as expected, shows “waiting…” repeatedly, then the outputs from the connectionCreated and updateEvent callbacks after I start the insitu side.

When I start the script in Jupyter, it shows

```auto
Accepting connection(s): myhost:22222
waiting...
waiting...
waiting...
...

```

… and the output stops when I start the insitu side.

Questions:

Do you have any idea, what interrupts \_monitorServerNotifications()? I also wrote the messages to a file to be sure that not the Jupyter output capturing is the problem.

How can I start debugging this problem?

I know that the problem may be the Jupyter side. But I assume that many of the Paraview community - at least the iparaview-kernel developers - have more insight into Jupyter than most Jupyter developers know about Paraview.

Thanks, Gregor

[catalystLiveVisualizer-debug.py](https://discourse.paraview.org/uploads/short-url/zWpFOTnAUzjP6sZGTpLR8QcUZNp.py) (1.8 KB)