[python] add support for exact client name

.chronus/changes/python-addExactSupport-2026-4-20-15-34-6.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-client-python"
+---
+
+add support for `exact` client names

packages/http-client-python/emitter/src/http.ts

@@ -29,6 +29,7 @@ import {
   camelToSnakeCase,
   emitParamBase,
   getAddedOn,
+  getClientName,
   getDelimiterAndExplode,
   getImplementation,
   isAbstract,
@@ -459,6 +460,7 @@ function emitFlattenedParameter(
     checkClientInput: false,
     clientDefaultValue: null,
     clientName: property.clientName,
+    isExactName: property.isExactName,
     delimiter: null,
     description: property.description,
     implementation: "Method",
@@ -622,7 +624,7 @@ function emitHttpBodyParameter(
     ...emitParamBase(context, bodyParam, undefined, serviceApiVersions),
     contentTypes: bodyParam.contentTypes,
     location: bodyParam.kind,
-    clientName: bodyParam.isGeneratedName ? "body" : camelToSnakeCase(bodyParam.name),
+    clientName: bodyParam.isGeneratedName ? "body" : getClientName(bodyParam),
     wireName: bodyParam.isGeneratedName ? "body" : bodyParam.name,
     implementation: getImplementation(context, bodyParam),
     clientDefaultValue: bodyParam.clientDefaultValue,

packages/http-client-python/emitter/src/types.ts

@@ -24,6 +24,7 @@ import {
   camelToSnakeCase,
   emitParamBase,
   getAddedOn,
+  getClientName,
   getClientNamespace,
   getImplementation,
 } from "./utils.js";
@@ -233,7 +234,8 @@ function emitProperty(
     addDisableGenerationMap(context, property.type);
   }
   return {
-    clientName: camelToSnakeCase(property.name),
+    clientName: getClientName(property),
+    isExactName: property.isExactName,
     wireName:
       (property.serializationOptions?.multipart
         ? property.serializationOptions?.multipart?.name

packages/http-client-python/emitter/src/utils.ts

@@ -107,6 +107,10 @@ export function camelToSnakeCase(name: string): string {
   return result_final;
 }
 
+export function getClientName(named: { name: string; isExactName: boolean }): string {
+  return named.isExactName ? named.name : camelToSnakeCase(named.name);
+}
+
 export function getImplementation(
   context: PythonSdkContext,
   parameter: SdkEndpointParameter | SdkCredentialParameter | SdkMethodParameter | SdkHttpParameter,
@@ -146,6 +150,7 @@ type ParamBase = {
   description: string;
   addedOn: string | undefined;
   clientName: string;
+  isExactName: boolean;
   inOverload: boolean;
   isApiVersion: boolean;
   type: Record<string, any>;
@@ -220,21 +225,22 @@ export function emitParamBase<TServiceOperation extends SdkServiceOperation>(
       });
     }
   }
-  let clientName = camelToSnakeCase(parameter.name);
+  let clientName = getClientName(parameter);
   if (
     parameter.kind !== "method" &&
     parameter.kind !== "credential" &&
     parameter.kind !== "endpoint" &&
     parameter.onClient &&
     parameter.correspondingMethodParams[0]
   ) {
-    clientName = camelToSnakeCase(parameter.correspondingMethodParams[0].name);
+    clientName = getClientName(parameter.correspondingMethodParams[0]);
   }
   return {
     optional: parameter.optional,
     description: (parameter.summary ? parameter.summary : parameter.doc) ?? "",
     addedOn: getAddedOn(context, parameter, serviceApiVersions),
     clientName,
+    isExactName: parameter.isExactName,
     inOverload: false,
     isApiVersion: parameter.isApiVersionParam,
     isContinuationToken:

packages/http-client-python/generator/pygen/codegen/models/operation.py

@@ -91,11 +91,16 @@ def __init__(
         self.has_etag: bool = self.yaml_data.get("hasEtag", False)
         self.cross_language_definition_id: Optional[str] = self.yaml_data.get("crossLanguageDefinitionId")
 
+    @property
+    def exact_name_params(self) -> set[str]:
+        """Return the set of client names for parameters with isExactName."""
+        return {p.client_name for p in self.parameters.method if p.is_exact_name}
+
     @property
     def stream_value(self) -> Union[str, bool]:
         return (
             f'kwargs.pop("stream", {self.has_stream_response})'
-            if self.expose_stream_keyword and self.has_response_body
+            if self.expose_stream_keyword and self.has_response_body and "stream" not in self.exact_name_params
             else self.has_stream_response
         )
 

packages/http-client-python/generator/pygen/codegen/models/parameter.py

@@ -87,6 +87,7 @@ def __init__(
         self.default_to_unset_sentinel: bool = self.yaml_data.get("defaultToUnsetSentinel", False)
         self.hide_in_method: bool = self.yaml_data.get("hideInMethod", False)
         self.is_continuation_token: bool = bool(self.yaml_data.get("isContinuationToken"))
+        self.is_exact_name: bool = self.yaml_data.get("isExactName", False)
 
     def get_declaration(self, value: Any = None) -> Any:
         return self.type.get_declaration(value)

packages/http-client-python/generator/pygen/codegen/serializers/builder_serializer.py

@@ -627,7 +627,8 @@ def _api_version_validation(self, builder: OperationType) -> str:
         return ""
 
     def pop_kwargs_from_signature(self, builder: OperationType) -> list[str]:
-        kwargs_to_pop = builder.parameters.kwargs_to_pop
+        exact_names = builder.exact_name_params
+        kwargs_to_pop = [k for k in builder.parameters.kwargs_to_pop if k.client_name not in exact_names]
         kwargs = self.parameter_serializer.pop_kwargs_from_signature(
             kwargs_to_pop,
             check_kwarg_dict=True,
@@ -645,7 +646,7 @@ def pop_kwargs_from_signature(self, builder: OperationType) -> list[str]:
             body_parameter=builder.parameters.body_parameter if builder.parameters.has_body else None,
         )
         for p in builder.parameters.parameters:
-            if p.hide_in_operation_signature and not p.is_continuation_token:
+            if p.hide_in_operation_signature and not p.is_continuation_token and p.client_name not in exact_names:
                 kwargs.append(f'{p.client_name} = kwargs.pop("{p.client_name}", None)')
         cls_annotation = builder.cls_type_annotation(
             async_mode=self.async_mode, serialize_namespace=self.serialize_namespace

packages/http-client-python/generator/pygen/preprocess/__init__.py

@@ -264,9 +264,10 @@ def update_types(self, yaml_data: list[dict[str, Any]]) -> None:
         for type in yaml_data:
             for property in type.get("properties", []):
                 property["description"] = update_description(property.get("description", ""))
-                property["clientName"] = self.pad_reserved_words(
-                    property["clientName"].lower(), PadType.PROPERTY, property
-                )
+                if not property.get("isExactName", False):
+                    property["clientName"] = self.pad_reserved_words(
+                        property["clientName"].lower(), PadType.PROPERTY, property
+                    )
                 add_redefined_builtin_info(property["clientName"], property)
             if type.get("name"):
                 pad_type = PadType.MODEL if type["type"] == "model" else PadType.ENUM_CLASS
@@ -362,14 +363,25 @@ def get_operation_updater(self, yaml_data: dict[str, Any]) -> Callable[[dict[str
 
     def update_parameter(self, yaml_data: dict[str, Any]) -> None:
         yaml_data["description"] = update_description(yaml_data.get("description", ""))
-        if not (yaml_data["location"] == "header" and yaml_data["clientName"] in ("content_type", "accept")):
+        if not yaml_data.get("isExactName", False) and not (
+            yaml_data["location"] == "header" and yaml_data["clientName"] in ("content_type", "accept")
+        ):
             yaml_data["clientName"] = self.pad_reserved_words(
                 yaml_data["clientName"].lower(), PadType.PARAMETER, yaml_data
             )
         if yaml_data.get("propertyToParameterName"):
             # need to create a new one with padded values (but NOT keys, since keys are wire names)
+            # build a lookup of exact-name properties from the body type's properties
+            exact_name_props = set()
+            for prop in yaml_data.get("type", {}).get("properties", []):
+                if prop.get("isExactName", False):
+                    exact_name_props.add(prop.get("wireName", ""))
             yaml_data["propertyToParameterName"] = {
-                prop: self.pad_reserved_words(param_name, PadType.PARAMETER, yaml_data).lower()
+                prop: (
+                    param_name
+                    if prop in exact_name_props
+                    else self.pad_reserved_words(param_name, PadType.PARAMETER, yaml_data).lower()
+                )
                 for prop, param_name in yaml_data["propertyToParameterName"].items()
             }
         wire_name_lower = (yaml_data.get("wireName") or "").lower()