As the title says, I am trying to use a key-value dictionary parameter to drive another parameter via an expression but I can't seem to make it work?


I haven't been able to find any information regarding this, I'm afraid.

Cheers
Jacob

The best you can do currently via Hscript Expressions is to use the chs function to get the entire value:

There is no way to directly get the value of a particular key.

In order to do that you would have to use a pythonexprs call to evaluate it as a dictionary in Python:

I have a method to read dict parm but must use Houdini 18.5's dict attribute and json function.

dict attr help [www.sidefx.com]

Now houdini does not have expression to deal with JSON, so you need a wrangle to convert JSON to dict attr…
And then use dict attr to drive another parm.

However, there are no JSON-parsing expression functions, and limited string manipulation functions, to deal with such a string in an expression.

JSON loads vex function [www.sidefx.com]

Thank you both of you for the answers.
I ended up using the pythonexprs solution but tested out the JSON one too just to learn some more :-)
one (unrelated) question zengchen, is there a deeper meaning why you use a string parameter ( ) instead of just directly using a string in ? just curious :-)

Cheers
Jacob

JacobAndersen
one (unrelated) question zengchen, is there a deeper meaning why you use a string parameter

houdini expression can only recognise two type - string(chs) and float(ch).
dict parm can not be interpreted as a float type, so it need to be treat as a string parameter, the result is a JSON format string, can be loads(loads is a function) as a dict attribute use vex function.

Hi, do you know how to do the reverse? I mean write the dictionary with python?

JohnFanny
Hi, do you know how to do the reverse? I mean write the dictionary with python?

You can set the hou.Parm directly with a dictionary, however all the keys and values will need to be strings.

Wow! Thanks a lot, it works perfectly! One last thing: Does it have a way to select one of the entries like in this example?