[python] fix pipeline client typing (#7119)

cc @kristapratico

---------

Co-authored-by: iscai-msft <[email protected]>

Author: iscai-msft

.chronus/changes/python-fixPipelineClientTyping-2025-3-24-12-12-49.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix typing for generic `PipelineClient`

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

@@ -64,7 +64,9 @@ def has_non_abstract_operations(self) -> bool:
         )
 
     def base_class(self, async_mode: bool) -> str:
-        pipeline_client = f"{'Async' if async_mode else ''}PipelineClient"
+        pipeline_client = (
+            f"{'Async' if async_mode else ''}PipelineClient[HttpRequest, {'Async' if async_mode else ''}HttpResponse]"
+        )
         base_classes: List[str] = []
         if self.is_mixin:
             base_classes.append(f"ClientMixinABC[{pipeline_client}, {self.client.name}Configuration]")
@@ -166,6 +168,16 @@ def imports(self, async_mode: bool, **kwargs: Any) -> FileImport:
                 "ClientMixinABC",
                 ImportType.LOCAL,
             )
+            file_import.add_submodule_import(
+                "rest",
+                "HttpRequest",
+                ImportType.SDKCORE,
+            )
+            file_import.add_submodule_import(
+                "rest",
+                f"{'Async' if async_mode else ''}HttpResponse",
+                ImportType.SDKCORE,
+            )
         else:
             file_import.add_msrest_import(
                 serialize_namespace=kwargs.get("serialize_namespace", self.code_model.namespace),