How can I get all materials which are using an ambient occlusion node?

Question

I'd like to get all materials using an ambient occlusion (AO) node and return their names in the console:

import bpy
mat = bpy.data.materials
for mat in mat:
    mat_name = (mat.name)
    ntree = mat.node_tree
    node = ntree.nodes.get("Ambient Occlusion", None)
if node is not None:
    print(&quot;Material With Ambient Occlusion:&quot;, mat_name)

It works fine for the start up file, but when I run it in another scene I get this error:

AttributeError: 'NoneType' object has no attribute 'nodes'

What is wrong? And why does the code only work for the start up file?

score 5 · Accepted Answer · edited Nov 20 '20 at 16:30

Not all materials have an associated node_tree. This is only present where the 'use_nodes' checkbox has been used as this creates the node tree.

Your problem is that one or more material does not have a node_tree. The solution is to include a test before the ntree.nodes.get() to first check that there is actually an attribute 'nodes' - and to simply skip that material if none is found:

import bpy
Run through all materials of the current blend file
for mat in bpy.data.materials:
    # If the material has a node tree
    if mat.node_tree:
        # Run through all nodes
        for node in mat.node_tree.nodes:
            # If the node type is Ambient Occlusion 
            if node.type == 'AMBIENT_OCCLUSION':
                # Print the name of the material
                print("Ambient Occlusion Node found in:", mat.name)

Thanks to @brockmann for the great edit to improve clarity. – Rich Sedman Nov 20 '20 at 16:34 — Rich Sedman, Nov 20 '20 at 16:34

How can I get all materials which are using an ambient occlusion node?

1 Answers1

Run through all materials of the current blend file

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