Add a driver to a material property using Python

Question

Is it possible to add a driver to a property in a shader using Python?

I managed to get driver_add working for other properties, but not shader properties. I can also print the property just fine.

selected_node = bpy.context.active_node
selected_node.driver_add("inputs[1].default_value", 0)

Do I need to format it differently for it to work?

The error message says

property "inputs[1].default_value" not found

The property itself is an input field of a Node Group I made by the way.

mat.node_tree.driver_add('nodes["My Node Name"].inputs[1].default_value', 0) — scurest, Commented Feb 22 at 19:46
@scurest have you tested it? Doesn't work for me: i.imgur.com/Zs8ROCi.png — Markus von Broady, Commented Feb 22 at 19:49
@MarkusvonBroady Quoted strings in fcurve data paths are "double quoted". — scurest, Commented Feb 22 at 20:13
@scurest I fall for this a 2nd time... Thanks :D But still, have you tried it? I don't get an error after fixing the quotes but the field still doesn't become purple. — Markus von Broady, Commented Feb 22 at 20:51
@MarkusvonBroady Yes, I have tried it. The field isn't purple because it isn't the "canonical" path to that datum, because you used a socket name instead of a number. Starting from a blank file, you can manually add a driver to a socket in the UI, then do D.materials[X].node_tree.animation_data.drivers[0].dath_path to see what data path Blender actually creates. — scurest, Commented Feb 22 at 21:37

Markus von Broady · Accepted Answer · 2024-02-22 19:46:58Z

4

Don't add a driver to the node, add it to the input:

D.materials['Material'].node_tree.nodes['Principled BSDF'].inputs['Roughness'].driver_add('default_value')

D is an alias in console for bpy.data

answered Feb 22 at 19:46

Markus von Broady

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