When one property of a key is set, all other (previously defined) properties of the key will be deleted. Example: Let's say we have set the following properties:
props.Set(pyluxcore.Property("scene.materials.test.type", "matte"))
props.Set(pyluxcore.Property("scene.materials.test.kd", [0.7, 0.7, 0.7]))
Now we want to set the material color to red. If we try the following, LuxCore will complain:
props.Set(pyluxcore.Property("scene.materials.test.kd", [0.8, 0, 0]))
This is because the line "scene.materials.test.type", "matte"
will be deleted and the material definition is missing the material type information.
You have to explicitly set lines you want to keep, even if they have not changed.