Allow Field.[de|]serialization_getter to be methods (as string argument)

Author: lafrech

src/marshmallow/fields.py

@@ -103,10 +103,10 @@ class _BaseFieldKwargs(typing.TypedDict, total=False):
     error_messages: types.ErrorMessages | None
     metadata: typing.Mapping[str, typing.Any] | None
     serialization_getter: (
-        typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
+        str | typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
     )
     deserialization_getter: (
-        typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
+        str | typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
     )
 
 
@@ -211,10 +211,10 @@ def __init__(
         error_messages: types.ErrorMessages | None = None,
         metadata: typing.Mapping[str, typing.Any] | None = None,
         serialization_getter: (
-            typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
+            str | typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
         ) = None,
         deserialization_getter: (
-            typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
+            str | typing.Callable[[typing.Any, str, typing.Any], typing.Any] | None
         ) = None,
     ) -> None:
         self.dump_default = dump_default
@@ -386,6 +386,14 @@ def _bind_to_schema(self, field_name: str, parent: Schema | Field) -> None:
         self.root = self.root or (
             self.parent.root if isinstance(self.parent, Field) else self.parent
         )
+        if isinstance(self.serialization_getter, str):
+            self.serialization_getter = utils.callable_or_raise(
+                getattr(parent, self.serialization_getter)
+            )
+        if isinstance(self.deserialization_getter, str):
+            self.deserialization_getter = utils.callable_or_raise(
+                getattr(parent, self.deserialization_getter)
+            )
 
     def _serialize(self, value: _InternalT | None, **kwargs) -> typing.Any:
         """Serializes ``value`` to a basic Python datatype. Noop by default.

tests/test_fields.py

@@ -151,6 +151,24 @@ def test_no_serialization_getter_falls_back_to_utils_get_value(self):
         field = fields.String()
         assert field.get_value({"name": "monty"}, "name") == "monty"
 
+    def test_serialization_getter_as_function(self):
+        def get_upper(obj, attr, default):
+            return obj[attr].upper()
+
+        class MySchema(Schema):
+            name = fields.String(serialization_getter=get_upper)
+
+        assert MySchema().dump({"name": "monty"}) == {"name": "MONTY"}
+
+    def test_serialization_getter_as_schema_method(self):
+        class MySchema(Schema):
+            def get_upper(self, obj, attr, default):
+                return obj[attr].upper()
+
+            name = fields.String(serialization_getter="get_upper")
+
+        assert MySchema().dump({"name": "monty"}) == {"name": "MONTY"}
+
     def test_deserialization_getter_overrides_default_access(self):
         class MySchema(Schema):
             name = fields.String(
@@ -199,6 +217,24 @@ class MySchema(Schema):
         result = MySchema().load({"name": "monty"})
         assert result == {"name": "monty"}
 
+    def test_deserialization_getter_as_function(self):
+        def get_upper(data, key, default):
+            return data[key].upper()
+
+        class MySchema(Schema):
+            name = fields.String(deserialization_getter=get_upper)
+
+        assert MySchema().load({"name": "monty"}) == {"name": "MONTY"}
+
+    def test_deserialization_getter_as_schema_method(self):
+        class MySchema(Schema):
+            def get_upper(self, data, key, default):
+                return data[key].upper()
+
+            name = fields.String(deserialization_getter="get_upper")
+
+        assert MySchema().load({"name": "monty"}) == {"name": "MONTY"}
+
 
 class TestParentAndName:
     class MySchema(Schema):