blender/doc/python_api/examples/bpy.app.handlers.1.py

"""
Persistent Handler Example
++++++++++++++++++++++++++

By default handlers are freed when loading new files, in some cases you may
wan't the handler stay running across multiple files (when the handler is
part of an addon for example).

For this the :data:`bpy.app.handlers.persistent` decorator needs to be used.
"""

import bpy
from bpy.app.handlers import persistent


@persistent
def load_handler(dummy):
    print("Load Handler:", bpy.data.filepath)

bpy.app.handlers.load_post.append(load_handler)