chore: refactor and __slots__ implementation for Base

Signed-off-by: Aaron Pham <29749331+aarnphm@users.noreply.github.com>

src/bentoml/_internal/io_descriptors/base.py

@@ -50,13 +50,44 @@ def from_spec(spec: dict[str, str]) -> IODescriptor[t.Any]:
     return IO_DESCRIPTOR_REGISTRY[spec["id"]].from_spec(spec)
 
 
-class IODescriptor(ABC, t.Generic[IOType]):
+class _OpenAPIMeta:
+    @abstractmethod
+    def openapi_schema(self) -> Schema | Reference:
+        raise NotImplementedError
+
+    @abstractmethod
+    def openapi_components(self) -> dict[str, t.Any] | None:
+        raise NotImplementedError
+
+    @abstractmethod
+    def openapi_example(self) -> t.Any | None:
+        raise NotImplementedError
+
+    @abstractmethod
+    def openapi_request_body(self) -> dict[str, t.Any]:
+        raise NotImplementedError
+
+    @abstractmethod
+    def openapi_responses(self) -> dict[str, t.Any]:
+        raise NotImplementedError
+
+
+class IODescriptor(ABC, _OpenAPIMeta, t.Generic[IOType]):
     """
     IODescriptor describes the input/output data format of an InferenceAPI defined
     in a :code:`bentoml.Service`. This is an abstract base class for extending new HTTP
     endpoint IO descriptor types in BentoServer.
     """
 
+    __slots__ = (
+        "_initialized",
+        "_args",
+        "_kwargs",
+        "_proto_fields",
+        "_mime_type",
+        "descriptor_id",
+    )
+
     HTTP_METHODS = ["POST"]
 
     descriptor_id: str | None
@@ -65,7 +96,9 @@ class IODescriptor(ABC, t.Generic[IOType]):
     _rpc_content_type: str = "application/grpc"
     _proto_fields: tuple[ProtoField]
     _sample: IOType | None = None
-    _set_sample: singledispatchmethod["IODescriptor[t.Any]"] = set_sample
+    _initialized: bool
+    _args: t.Sequence[t.Any]
+    _kwargs: dict[str, t.Any]
 
     def __init_subclass__(cls, *, descriptor_id: str | None = None):
         if descriptor_id is not None:
@@ -75,17 +108,35 @@ def __init_subclass__(cls, *, descriptor_id: str | None = None):
                 )
             IO_DESCRIPTOR_REGISTRY[descriptor_id] = cls
         cls.descriptor_id = descriptor_id
+        cls._initialized = False
 
     def __new__(cls, *args: t.Any, **kwargs: t.Any) -> Self:
         sample = kwargs.pop("_sample", None)
-        kls = object.__new__(cls)
+        klass = object.__new__(cls)
         if sample is None:
             set_sample.register(type(None), lambda self, _: self)
-        kls = kls._set_sample(sample)
-        # TODO: lazy init
-        kls.__init__(*args, **kwargs)
+        kls = klass._set_sample(sample)
+        kls._args = args
+        kls._kwargs = kwargs
         return kls
 
+    def __getattr__(self, name: str) -> t.Any:
+        if not self._initialized:
+            self._lazy_init()
+        assert self._initialized
+        return getattr(self, name)
+
+    def __repr__(self) -> str:
+        return self.__class__.__qualname__
+
+    def _lazy_init(self) -> None:
+        self.__init__(*self._args, **self._kwargs)
+        self._initialized = True
+        del self._args
+        del self._kwargs
+
+    _set_sample: singledispatchmethod[IODescriptor[t.Any]] = set_sample
+
     @property
     def sample(self) -> IOType | None:
         return self._sample
@@ -114,33 +165,10 @@ def to_spec(self) -> dict[str, t.Any]:
     def from_spec(cls, spec: dict[str, t.Any]) -> Self:
         raise NotImplementedError
 
-    def __repr__(self) -> str:
-        return self.__class__.__qualname__
-
     @abstractmethod
     def input_type(self) -> InputType:
         raise NotImplementedError
 
-    @abstractmethod
-    def openapi_schema(self) -> Schema | Reference:
-        raise NotImplementedError
-
-    @abstractmethod
-    def openapi_components(self) -> dict[str, t.Any] | None:
-        raise NotImplementedError
-
-    @abstractmethod
-    def openapi_example(self) -> t.Any | None:
-        raise NotImplementedError
-
-    @abstractmethod
-    def openapi_request_body(self) -> dict[str, t.Any]:
-        raise NotImplementedError
-
-    @abstractmethod
-    def openapi_responses(self) -> dict[str, t.Any]:
-        raise NotImplementedError
-
     @abstractmethod
     async def from_http_request(self, request: Request) -> IOType:
         ...