Copy the `material_index` attribute between identical meshes in Blender. Makes it possible to copy per-face material assignments between meshes.

copy_material_index.py

import bpy

# Get the active object
active_obj = bpy.context.active_object

# Get all selected objects
selected_objs = bpy.context.selected_objects

# Check that active object is a mesh
if active_obj.type != 'MESH':
    print("Active object is not a mesh")
else:
    # Copy the material_index from each face of active object to the corresponding face of each selected object
    for obj in selected_objs:
        if obj.type == 'MESH':
            for face in range(len(active_obj.data.polygons)):
                obj.data.polygons[face].material_index = active_obj.data.polygons[face].material_index