fix(python): apply defaults only to query params, not to request body properties

generators/python/sdk/versions.yml

@@ -1,5 +1,14 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
 # For unreleased changes, use unreleased.yml
+- version: 4.54.4
+  changelogEntry:
+    - summary: |
+        The `use_provided_defaults` config option no longer applies defaults to
+        inlined request body parameters.
+      type: fix
+  createdAt: "2026-02-05"
+  irVersion: 62
+
 - version: 4.54.3
   changelogEntry:
     - summary: |

generators/python/src/fern_python/generators/context/pydantic_generator_context.py

@@ -115,7 +115,7 @@ def get_type_names_in_type_reference(self, type_reference: ir_types.TypeReferenc
 
     @abstractmethod
     def get_initializer_for_type_reference(
-        self, type_reference: ir_types.TypeReference
+        self, type_reference: ir_types.TypeReference, *, for_request_param: bool = False
     ) -> Optional[AST.Expression]: ...
 
     @abstractmethod

generators/python/src/fern_python/generators/context/pydantic_generator_context_impl.py

@@ -89,13 +89,16 @@ def get_initializer_for_type_reference(
         self,
         type_reference: ir_types.TypeReference,
         ignore_literals: bool = False,
+        *,
+        for_request_param: bool = False,
     ) -> Optional[AST.Expression]:
         default_value = None
         union = type_reference.get_as_union()
 
         # Only populate primitive defaults if we're allowed to leverage them via config
-        # Otherwise we want to be able to generate defaults for literals, and aliases of literals
-        if union.type == "primitive" and self._allow_leveraging_defaults:
+        # AND this is for a request param (query param or header). Request body properties
+        # and Pydantic model fields should not get primitive defaults.
+        if union.type == "primitive" and self._allow_leveraging_defaults and for_request_param:
             maybe_v2_scheme = union.primitive.v_2
             if maybe_v2_scheme is not None:
                 default_value = maybe_v2_scheme.visit(
@@ -116,7 +119,9 @@ def get_initializer_for_type_reference(
         elif union.type == "named":
             type_declaration = self.get_declaration_for_type_id(union.type_id)
             default_value = type_declaration.shape.visit(
-                alias=lambda a: self.get_initializer_for_type_reference(a.alias_of, ignore_literals=ignore_literals),
+                alias=lambda a: self.get_initializer_for_type_reference(
+                    a.alias_of, ignore_literals=ignore_literals, for_request_param=for_request_param
+                ),
                 enum=lambda _: None,
                 object=lambda _: None,
                 union=lambda _: None,
@@ -133,8 +138,12 @@ def get_initializer_for_type_reference(
                 list_=lambda _: None,
                 set_=lambda _: None,
                 # Ignore literal defaults when the wrapping type is optional
-                optional=lambda opt: self.get_initializer_for_type_reference(opt, ignore_literals=True),
-                nullable=lambda nullable: self.get_initializer_for_type_reference(nullable, ignore_literals=True),
+                optional=lambda opt: self.get_initializer_for_type_reference(
+                    opt, ignore_literals=True, for_request_param=for_request_param
+                ),
+                nullable=lambda nullable: self.get_initializer_for_type_reference(
+                    nullable, ignore_literals=True, for_request_param=for_request_param
+                ),
                 map_=lambda _: None,
             )
 

generators/python/src/fern_python/generators/sdk/client_generator/endpoint_function_generator.py

@@ -422,7 +422,7 @@ def _get_endpoint_named_parameters(
                         docs=query_parameter.docs,
                         type_hint=self._get_typehint_for_query_param(query_parameter, query_parameter_type_hint),
                         initializer=self._context.pydantic_generator_context.get_initializer_for_type_reference(
-                            query_parameter.value_type
+                            query_parameter.value_type, for_request_param=True
                         ),
                     ),
                 )

generators/python/src/fern_python/generators/sdk/client_generator/request_body_parameters/inlined_request_body_parameters.py

@@ -39,9 +39,6 @@ def get_parameters(self, names_to_deconflict: Optional[List[str]] = None) -> Lis
                     property.value_type,
                     in_endpoint=True,
                 )
-                maybe_default_value = self._context.pydantic_generator_context.get_initializer_for_type_reference(
-                    property.value_type,
-                )
                 parameters.append(
                     AST.NamedFunctionParameter(
                         name=self._get_property_name(property),
@@ -50,9 +47,7 @@ def get_parameters(self, names_to_deconflict: Optional[List[str]] = None) -> Lis
                             property.value_type,
                             in_endpoint=True,
                         ),
-                        initializer=maybe_default_value
-                        if maybe_default_value is not None
-                        else AST.Expression(DEFAULT_BODY_PARAMETER_VALUE)
+                        initializer=AST.Expression(DEFAULT_BODY_PARAMETER_VALUE)
                         if type_hint.is_optional
                         else None,
                         raw_type=property.value_type,