Add functionality to existing commands

Question

I want to update my import .fbx, so it would replace and remove all duplicate materials. I have found how to do the action at: link

However, I don't really want to create my whole custom import .fbx that would basically do the same thing as the regular import, but also execute this at the end.

Is there a way I could piggyback my custom code onto existing functions? Meaning my addon script would only be:

def at_import_fbx_end():
    do_my_stuff()

Or something similar to this.

Answer 1

You can piggyback on an operator by declaring another operator that uses the same bl_idname. It's a common gotcha that we can use to our advantage. It's a hack and it might mess up things when you unregister, but nothing that you can't repair in a few minutes by replacing the script files.

This script will for instance apply a translation to all imported objects :

import bpy
from bpy_extras.io_utils import ImportHelper

import io_scene_fbx


class SimpleOperator(bpy.types.Operator, ImportHelper):
    bl_idname = "import_scene.fbx"  # Overwrite the base operator
    bl_label = "FBX override"

    def execute(self, context):
        # You can do things before importing
        io_scene_fbx.ImportFBX.execute(self, context)
        # You can do things after importing
        bpy.ops.transform.translate(value=(0, 0, 5))
        return {"FINISHED"}

# We steal the importer settings. However the display will be messed up :
SimpleOperator.__annotations__.update(io_scene_fbx.ImportFBX.__annotations__)  

def register():
    bpy.utils.register_class(SimpleOperator)


def unregister():
    bpy.utils.unregister_class(SimpleOperator)
    bpy.utils.register_class(io_scene_fbx.ImportFBX)


if __name__ == "__main__":
    register()

Answer 2

I just had a quick look and if you right click on any menu operator you can access certain shortcuts, including the Python command for it. See image:

(To enable this function, you need to enable Python tooltips in Interface preferences > Display > Python Tooltips)

So for this example, your script could start with bpy.ops.import_scene.fbx(), then you add do_my_stuff() afterwards. (I clicked the copy command from the shown UI button for that code)

It may be that in order to combine these in a way that works, you'll need to add a custom UI panel or something where you can choose which file to import and then let your code run, removing duplicate materials once you've imported it.

As far as I know, Blender does not contain any signals for finishing things like file imports or other processes.