user: How do I use Note on Altering Data in Blender? Include parameters, examples, warnings and best practices.

assistant: Altering data from handlers should be done carefully. While rendering the
`frame_change_pre` and `frame_change_post` handlers are called from one
thread and the viewport updates from a different thread. If the handler changes
data that is accessed by the viewport, this can cause a crash of Blender. In
such cases, lock the interface (Render → Lock Interface or
[`bpy.types.RenderSettings.use_lock_interface`](bpy.types.RenderSettings.html#bpy.types.RenderSettings.use_lock_interface "bpy.types.RenderSettings.use_lock_interface")) before starting a render.

Below is an example of a mesh that is altered from a handler:

```
def frame_change_pre(scene):
    # A triangle that shifts in the z direction.
    zshift = scene.frame_current * 0.1
    vertices = [(-1, -1, zshift), (1, -1, zshift), (0, 1, zshift)]
    triangles = [(0, 1, 2)]

    object = bpy.data.objects["The Object"]
    object.data.clear_geometry()
    object.data.from_pydata(vertices, [], triangles)
```

bpy.app.handlers.animation_playback_post
:   on ending animation playback. Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.animation_playback_pre
:   on starting animation playback. Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.annotation_post
:   on drawing an annotation (after). Accepts two arguments: the annotation data-block and dependency graph

bpy.app.handlers.annotation_pre
:   on drawing an annotation (before). Accepts two arguments: the annotation data-block and dependency graph

bpy.app.handlers.blend_import_post
:   on linking or appending data (after). Accepts one argument: a BlendImportContext

bpy.app.handlers.blend_import_pre
:   on linking or appending data (before). Accepts one argument: a BlendImportContext

bpy.app.handlers.composite_cancel
:   on a compositing background job (cancel). Accepts one argument: the scene data-block

bpy.app.handlers.composite_post
:   on a compositing background job (after). Accepts one argument: the scene data-block

bpy.app.handlers.composite_pre
:   on a compositing background job (before). Accepts one argument: the scene data-block

bpy.app.handlers.depsgraph_update_post
:   on depsgraph update (post). Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.depsgraph_update_pre
:   on depsgraph update (pre). Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.frame_change_post
:   Called after frame change for playback and rendering, after the data has been evaluated for the new frame. Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.frame_change_pre
:   Called after frame change for playback and rendering, before any data is evaluated for the new frame. This makes it possible to change data and relations (for example swap an object to another mesh) for the new frame. Note that this handler is **not** to be used as ‘before the frame changes’ event. The dependency graph is not available in this handler, as data and relations may have been altered and the dependency graph has not yet been updated for that. Accepts two arguments: The scene data-block and the dependency graph being updated

bpy.app.handlers.load_factory_preferences_post
:   on loading factory preferences (after)

bpy.app.handlers.load_factory_startup_post
:   on loading factory startup (after)

bpy.app.handlers.load_post
:   on loading a new blend file (after). Accepts one argument: the file being loaded, an empty string for the startup-file.

bpy.app.handlers.load_post_fail
:   on failure to load a new blend file (after). Accepts one argument: the file being loaded, an empty string for the startup-file.

bpy.app.handlers.load_pre
:   on loading a new blend file (before).Accepts one argument: the file being loaded, an empty string for the startup-file.

bpy.app.handlers.object_bake_cancel
:   on canceling a bake job; will be called in the main thread. Accepts one argument: the object data-block being baked

bpy.app.handlers.object_bake_complete
:   on completing a bake job; will be called in the main thread. Accepts one argument: the object data-block being baked

bpy.app.handlers.object_bake_pre
:   before starting a bake job. Accepts one argument: the object data-block being baked

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. Accepts one argument: the scene data-block being rendered

bpy.app.handlers.render_complete
:   on completion of render job. Accepts one argument: the scene data-block being rendered

bpy.app.handlers.render_init
:   on initialization of a render job. Accepts one argument: the scene data-block being rendered

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. Accepts one argument: the render stats (render/saving time plus in background mode frame/used [peak] memory).

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). Accepts one argument: the file being saved, an empty string for the startup-file.

bpy.app.handlers.save_post_fail
:   on failure to save a blend file (after). Accepts one argument: the file being saved, an empty string for the startup-file.

bpy.app.handlers.save_pre
:   on saving a blend file (before). Accepts one argument: the file being saved, an empty string for the startup-file.

bpy.app.handlers.translation_update_post
:   on translation settings update

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.xr_session_start_pre
:   on starting an xr session (before)

bpy.app.handlers.persistent
:   Function decorator for callback functions not to be removed when loading new files