# SaveManager

Save, load and migrate persisted Properties

```{raw} html
<a class="example-run-button" href="../demos/features_basics_save_load.html">▶ Run in browser</a>


```

**Tags:** `basics` `save` `load` `persistence` `property`

A player disc carries its position, score and colour as ``Property(persist=True)``
values. S snapshots the whole tree to slot1 through ``SaveManager`` and L loads it
back and applies it, restoring exactly the persisted state. The player class is at
``__save_version__ = 2`` and ships a ``__migrate_save__`` hook that upgrades a
version-1 payload (which stored the score under an old name) on apply.

Saves land in a fresh ``tempfile.mkdtemp()`` directory so this example never
writes into the repository; a real game would point ``SaveManager`` at its own
saves directory under the user's data dir instead.


## What it demonstrates
- `Property(persist=True)`: only flagged Properties enter the snapshot.
- `SaveManager(save_dir)`: `save(root, "slot1")`, `load("slot1")`, `apply(root, data)`.
- Restoring live state: position, score and colour snap back on load.
- `__save_version__` + `__migrate_save__(values, from_v, to_v)`: upgrading an
  old payload on apply (exercised by the selftest).

Controls:
  Arrow keys - Move the player
  SPACE      - Score points
  C          - Cycle the player colour
  S          - Save to slot1
  L          - Load slot1 and apply it
  ESC        - Quit

Run: uv run python examples/features/basics/save_load.py
Headless self-check: uv run python examples/features/basics/save_load.py --test

## Source

```{literalinclude} ../../examples/features/basics/save_load.py
:language: python
:linenos:
```