Hi there
I have very strange stuff happening with python parameter expressions [www.sidefx.com] in string parameters

Basically it seems completly random weither the expression will compute or not. Sometimes the expression will just stay as plain text (the parameter does not become blue), sometimes it does work immediatly.

I've done dozen of HDA for my company, but I still can't find a way to make this work everytime. This is always the one thing that takes me the most time.


Is there a specific thing to do with the interface when adding the python expression? I usually clic in the parameter, alt+e, type my expression then clic "apply" in the houdini edit string window. It does not work.
Doing a right clic on the parameter > Expression > Toggle Expression does not work either.

See exemples of problems in the screenshot:

1/
- string_b should compute and return "exemple text" from string_a
- string_c does compute and return "exemple text" from string_a, but is using `chs()` rather than hou.evalParm()
- string_d does not compute and return "EXEMPLE TEXT"

2/ string_toggle_a should compute and return "toggle is 0"
2/ string_toggle_b should compute and return "toggle is 0"


Can anyone help me on this ?

Try to force set a keyframe with alt+lmb on the parameter and then write the python expression.
See if this helps

its not random, there are certain rules to in which mode the Alt+E editor is opened

but regardless of the initial mode you can easily change it at the bottom
so just make sure it says Python Expression or depending on what you want (Hscript Expression, String)

as to the rules I observed (which may still be the useful for Houdini that don't have that choice exposed yet):
if your parameter is showing raw value (highlighted label) Alt+E will open in Edit Expression mode, using the current nodes language
otherwise it opens as Edit String

Andr
Try to force set a keyframe with alt+lmb on the parameter and then write the python expression.
See if this helps

That did the trick, thanks a lot!

tamte
but regardless of the initial mode you can easily change it at the bottom
so just make sure it says Python Expression or depending on what you want (Hscript Expression, String)

Is it a feature in the latest version of houdini ? I'm on 19.0.5 and can't find it in the Edit String/Expression window

BenWall
Is it a feature in the latest version of houdini ? I'm on 19.0.5 and can't find it in the Edit String/Expression window

I think it was added in 19.5

the Edit String/Expression window was renamed to just Edit
so if it still says Edit String/Expression than you dont have that feature and you can follow the described rules and see if it holds up for you

when you open the editor, there is a drop-down menu at the bottom to select text type.