feat(persistent_data): pure-Python counterpart (espp.persistent_data)

components/persistent_data/README.md

@@ -210,6 +210,46 @@ settings file, or for host-side tests of migrations. It is not in the Python
 bindings: `PersistentData` is a class template over the application's own
 types, which the generated bindings cannot instantiate generically.
 
+## Python
+
+The espp Python package ships `espp.persistent_data`, a pure-Python (stdlib
+only) counterpart that reads and writes the same files: schema versions are
+dataclasses, newest first, with width aliases for the numeric fields and a
+`migrate()` classmethod per version, exactly mirroring the C++ type list. The
+layout fingerprint is derived from the annotations by the grammar above, so a
+file written in Python verifies on the device and vice versa.
+
+```python
+from dataclasses import dataclass, field
+from typing import ClassVar
+from espp.persistent_data import PersistentData, u8, u32, f32
+
+@dataclass
+class SettingsV1:
+    VERSION: ClassVar[int] = 1
+    brightness: u8 = 50
+    device_name: str = "espp"
+
+@dataclass
+class Settings:
+    VERSION: ClassVar[int] = 2
+    device_name: str = "espp"
+    brightness: f32 = 0.5
+    favorites: list[str] = field(default_factory=list)
+
+    @classmethod
+    def migrate(cls, v1: SettingsV1) -> "Settings":
+        return cls(device_name=v1.device_name, brightness=v1.brightness / 100)
+
+settings = PersistentData([Settings, SettingsV1], "settings.bin")
+data = settings.load_or_create(Settings())        # migrates a v1 file and rewrites it
+settings.update(lambda s: s.favorites.append("red"))
+```
+
+Errors are `PersistentDataError` with an `errc` matching `PersistentDataErrc`.
+The codec is byte-checked against vectors generated by the C++ codec in
+`python/persistent_data_test.py`.
+
 ## Host test
 
 The file format, version list, migration chain and file helpers live in

lib/python_bindings/espp/__init__.py

@@ -12,6 +12,10 @@
 # ``espp.rtps.Publisher`` / ``espp.rtps.Subscriber``).
 from . import rtps  # noqa: F401,E402
 
+# Pure-Python counterpart of the persistent_data component: reads / writes the
+# firmware's versioned settings files from dataclasses (``espp.persistent_data``).
+from . import persistent_data  # noqa: F401,E402
+
 # The pure-python ODrive legacy-native protocol CLIENT (espp_odrive, sourced
 # from components/odrive_native/python) ships alongside this package in the
 # wheel / installed prefix; expose it as ``espp.odrive`` for convenience. The