Application Handlers (bpy.app.handlers)

This module contains callback lists

Basic Handler Example

This script shows the most simple example of adding a handler.

import bpy


def my_handler(scene):
    print("Frame Change", scene.frame_current)


bpy.app.handlers.frame_change_pre.append(my_handler)

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 add-on for example).

For this the 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)

bpy.app.handlers.frame_change_post

on frame change for playback and rendering (after)

bpy.app.handlers.frame_change_pre

on frame change for playback and rendering (before)

bpy.app.handlers.game_post

on ending the game engine

bpy.app.handlers.game_pre

on starting the game engine

bpy.app.handlers.load_post

on loading a new blend file (after)

bpy.app.handlers.load_pre

on loading a new blend file (before)

bpy.app.handlers.redo_post

on loading a redo step (after)

bpy.app.handlers.redo_pre

on loading a redo step (before)

bpy.app.handlers.render_cancel

on canceling a render job

bpy.app.handlers.render_complete

on completion of render job

bpy.app.handlers.render_init

on initialization of a render job

bpy.app.handlers.render_post

on render (after)

bpy.app.handlers.render_pre

on render (before)

bpy.app.handlers.render_stats

on printing render statistics

bpy.app.handlers.render_write

on writing a render frame (directly after the frame is written)

bpy.app.handlers.save_post

on saving a blend file (after)

bpy.app.handlers.save_pre

on saving a blend file (before)

bpy.app.handlers.scene_update_post

on every scene data update. Does not imply that anything changed in the scene, just that the dependency graph was reevaluated, and the scene was possibly updated by Blender’s animation system.

bpy.app.handlers.scene_update_pre

on every scene data update. Does not imply that anything changed in the scene, just that the dependency graph is about to be reevaluated, and the scene is about to be updated by Blender’s animation system.

bpy.app.handlers.undo_post

on loading an undo step (after)

bpy.app.handlers.undo_pre

on loading an undo step (before)

bpy.app.handlers.version_update

on ending the versioning code

bpy.app.handlers.persistent

Function decorator for callback functions not to be removed when loading new files