✨ Add main GenericSchema class

src/marshmallow_generic/schema.py

@@ -0,0 +1,68 @@
+"""Definition of the `GenericSchema` base class."""
+
+from collections.abc import Iterable, Mapping, Sequence
+from typing import TYPE_CHECKING, Any, Literal, Optional, TypeVar, Union, overload
+
+from marshmallow import Schema
+
+from ._util import GenericInsightMixin
+from .decorators import post_load
+
+_T = TypeVar("_T")
+
+
+class GenericSchema(GenericInsightMixin[_T], Schema):
+    """
+    Schema parameterized by the class it deserializes data to.
+
+    Registers a `post_load` hook to pass validated data to the constructor
+    of the specified class.
+
+    Requires a specific (non-generic) class to be passed as the type argument
+    for deserialization to work properly.
+    """
+
+    @post_load
+    def instantiate(self, data: dict[str, Any], **_kwargs: Any) -> _T:
+        """Unpacks `data` into the constructor of the specified type."""
+        return self._get_type_arg()(**data)
+
+    if TYPE_CHECKING:
+
+        @overload  # type: ignore[override]
+        def load(
+            self,
+            data: Union[Mapping[str, Any], Iterable[Mapping[str, Any]]],
+            *,
+            many: Literal[True],
+            partial: Union[bool, Sequence[str], set[str], None] = None,
+            unknown: Optional[str] = None,
+        ) -> list[_T]:
+            ...
+
+        @overload
+        def load(
+            self,
+            data: Union[Mapping[str, Any], Iterable[Mapping[str, Any]]],
+            *,
+            many: Optional[Literal[False]] = None,
+            partial: Union[bool, Sequence[str], set[str], None] = None,
+            unknown: Optional[str] = None,
+        ) -> _T:
+            ...
+
+        def load(
+            self,
+            data: Union[Mapping[str, Any], Iterable[Mapping[str, Any]]],
+            *,
+            many: Optional[bool] = None,
+            partial: Union[bool, Sequence[str], set[str], None] = None,
+            unknown: Optional[str] = None,
+        ) -> Union[list[_T], _T]:
+            """
+            Same as `marshmallow.Schema.load` at runtime.
+
+            Annotations ensure that type checkers will infer the return type
+            correctly based on the type argument passed to a specific subclass.
+            """
+            ...

tests/test_schema.py

@@ -0,0 +1,37 @@
+from unittest import TestCase
+from unittest.mock import MagicMock, patch
+
+from marshmallow_generic import _util, schema
+
+
+class GenericSchemaTestCase(TestCase):
+    @patch.object(_util.GenericInsightMixin, "_get_type_arg")
+    def test_instantiate(self, mock__get_type_arg: MagicMock) -> None:
+        mock__get_type_arg.return_value = mock_cls = MagicMock()
+        mock_data = {"foo": "bar", "spam": 123}
+
+        class Foo:
+            pass
+
+        schema_obj = schema.GenericSchema[Foo]()
+        # Explicit annotation to possibly catch mypy errors:
+        output: Foo = schema_obj.instantiate(mock_data)
+        self.assertIs(mock_cls.return_value, output)
+        mock__get_type_arg.assert_called_once_with()
+        mock_cls.assert_called_once_with(**mock_data)
+
+    def test_load(self) -> None:
+        """Mainly for static type checking purposes."""
+
+        class Foo:
+            pass
+
+        class TestSchema(schema.GenericSchema[Foo]):
+            pass
+
+        single: Foo = TestSchema().load({})
+        self.assertIsInstance(single, Foo)
+
+        multiple: list[Foo] = TestSchema().load([{}], many=True)
+        self.assertIsInstance(multiple, list)
+        self.assertIsInstance(multiple[0], Foo)