bpy do something every time an object is added

Question

How can I make a condition for every time a new object is added to the scene? Example: Every time an object is added, it's given a triangulate modifier?

Answer 1

As @Psyonic has mentioned: You can monitor the dependency graph with a handler, and every time it is updated compare an old list of objects to the current list of objects. And if a new one is found add your modifier to it.

Here's the working script:

import bpy
bpy.app.handlers.depsgraph_update_post.clear()
previous_objects = set(bpy.data.objects)
def add_triangulate_modifier(obj):
    for mod in obj.modifiers:
        if mod.type == "TRIANGULATE":
            return
    mod = obj.modifiers.new(name="Triangulate", type='TRIANGULATE')
def new_object_added(scene):
    global previous_objects
current_objects = set(bpy.data.objects)
new_objects = current_objects - previous_objects
previous_objects = current_objects

if not new_objects:
    return

for obj in new_objects:
    print("New object added: ", obj.name, type(obj))
    add_triangulate_modifier(obj)


bpy.app.handlers.depsgraph_update_post.append(new_object_added)