refactor(core): improve beta decorator (#32505)

This is better than using a subclass as returning a `property` works
with `ClassWithBetaMethods.beta_property.__doc__`

Co-authored-by: Mason Daugherty <mason@langchain.dev>

libs/core/langchain_core/_api/beta_decorator.py

@@ -156,50 +156,24 @@ def beta(
             _name = _name or obj.fget.__qualname__
             old_doc = obj.__doc__
 
-            class _BetaProperty(property):
+            def _fget(instance: Any) -> Any:
-                """A beta property."""
-
-                def __init__(
-                    self,
-                    fget: Union[Callable[[Any], Any], None] = None,
-                    fset: Union[Callable[[Any, Any], None], None] = None,
-                    fdel: Union[Callable[[Any], None], None] = None,
-                    doc: Union[str, None] = None,
-                ) -> None:
-                    super().__init__(fget, fset, fdel, doc)
-                    self.__orig_fget = fget
-                    self.__orig_fset = fset
-                    self.__orig_fdel = fdel
-                    self.__doc__ = doc
-
-                def __get__(
-                    self, instance: Any, owner: Union[type, None] = None
-                ) -> Any:
-                    if instance is not None or owner is not None:
-                        emit_warning()
-                    return self.fget(instance)
-
-                def __set__(self, instance: Any, value: Any) -> None:
                 if instance is not None:
                     emit_warning()
-                    return self.fset(instance, value)
+                return obj.fget(instance)
 
-                def __delete__(self, instance: Any) -> None:
+            def _fset(instance: Any, value: Any) -> None:
                 if instance is not None:
                     emit_warning()
-                    return self.fdel(instance)
+                obj.fset(instance, value)
 
-                def __set_name__(self, owner: Union[type, None], set_name: str) -> None:
+            def _fdel(instance: Any) -> None:
-                    nonlocal _name
+                if instance is not None:
-                    if _name == "<lambda>":
+                    emit_warning()
-                        _name = set_name
+                obj.fdel(instance)
 
-            def finalize(wrapper: Callable[..., Any], new_doc: str) -> Any:  # noqa: ARG001
+            def finalize(_wrapper: Callable[..., Any], new_doc: str) -> Any:
                 """Finalize the property."""
-                return _BetaProperty(
+                return property(fget=_fget, fset=_fset, fdel=_fdel, doc=new_doc)
-                    fget=obj.fget, fset=obj.fset, fdel=obj.fdel, doc=new_doc
-                )
-
         else:
             _name = _name or obj.__qualname__
             if not _obj_type:

libs/core/tests/unit_tests/_api/test_beta_decorator.py

@@ -91,12 +91,20 @@ class ClassWithBetaMethods:
         """Original doc."""
         return "This is a beta staticmethod."
 
-    @beta()  # type: ignore[prop-decorator]
     @property
     def beta_property(self) -> str:
         """Original doc."""
         return "This is a beta property."
 
+    @beta_property.setter
+    def beta_property(self, _value: str) -> None:
+        pass
+
+    @beta()  # type: ignore[misc]
+    @beta_property.deleter
+    def beta_property(self) -> None:
+        pass
+
 
 def test_beta_function() -> None:
     """Test beta function."""
@@ -222,14 +230,17 @@ def test_beta_property() -> None:
         obj = ClassWithBetaMethods()
         assert obj.beta_property == "This is a beta property."
 
-        assert len(warning_list) == 1
+        obj.beta_property = "foo"
-        warning = warning_list[0].message
 
-        assert str(warning) == (
+        del obj.beta_property
+
+        assert len(warning_list) == 3
+        for warning in warning_list:
+            assert str(warning.message) == (
                 "The attribute `ClassWithBetaMethods.beta_property` is in beta. "
                 "It is actively being worked on, so the API may change."
             )
-        doc = ClassWithBetaMethods.__dict__["beta_property"].__doc__
+        doc = ClassWithBetaMethods.beta_property.__doc__
         assert isinstance(doc, str)
         assert doc.startswith(".. beta::")