Python state question:
Has anybody noticed issues with onParmChangeEvent? For context: I am using the function in an HDA interactive script that otherwise works fine.

Do I need something besides defining the function to make it work? I put a print function in it and am manipulating parameters and the function does not seem to trigger.

Any ideas of what I might be missing?

Documentation has an example about this.
Did you check it out?
https://www.sidefx.com/docs/houdini/hom/state_parameters.html#binding-the-parameter [www.sidefx.com]

Yes, thank you, but when I run the test scene ( $HH/viewer_states/examples/state_parms_demo.hip ) and put a print in the onParmChangeEvent I still see nothing getting printed.

That aside, the function seems to work, so I am definitely missing something.
Gonna try to report it as a bug and see what they tell me.

I tested the example file which you've mentioned and it worked for me!
I put a print function as you said in onParmChangeEvent and after changing settings from operation toolbar, print function called successfully!
BTW if you expect to trigger this function whenever you change a parameter via parameter editor pane, you should use callback script instead.