# 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 addon 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.``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 updating the scenes data (after)

`bpy.app.handlers.``scene_update_pre`

  on updating the scenes data (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