Python - Component dataclasses as class properties

components.py

from dataclasses import dataclass, field, fields, replace, asdict

_MISSING = object()

@dataclass
class Component(object):
    """
    Collection of attributes.
    """
    _key: str = field(default=None, hash=False, repr=False, compare=False)
    _entity:object = field(default=None, hash=False, repr=False, compare=False)
    autosave:bool = field(default=False, hash=False, repr=False, compare=False)

    def __set_name__(self, owner, name):
        self._key = name

    def __get__(self, instance, owner):
        # Try getting existing component object
        obj = getattr(instance.ndb, self._key, _MISSING)
        if obj and isinstance(obj, self.__class__):
            return obj

        # Try getting data from db
        data = getattr(instance.db, self._key, {})

        # Create and save new object to ndb
        obj = replace(self, _entity=instance, **data)
        setattr(instance.ndb, self._key, obj)
        return obj

    def __setattr__(self, key, value):
        super().__setattr__(key, value)
        if self.autosave: self.save()

    def save(self):
        base_fields = tuple(f.name for f in fields(Component))
        data = {k:v for k,v in asdict(self).items() if k not in base_fields}
        setattr(self._entity.db, self._key, data)

@dataclass
class Geometry(Component):
    height:float = 0.0
    width:float = 0.0
    depth:float = 0.0

class DB(object): pass
class Object(object):

    geom = Geometry(depth=16)

    def __init__(self):
        self.db = DB()
        self.ndb = DB()

o = Object()
o.geom.height = 5.0

print(o, o.geom, o.geom.height)
o.geom.save()
print(o.db.geom)

o3 = Object()
print(o3.geom)