[python] Fix @clientDefaultValue serialization regression from #10476

.chronus/changes/python-fix-client-default-value-serialization-2026-4-29-10-23-0.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix serialization regression where `@clientDefaultValue` defaults on model properties were no longer included in the request body. Defaults are again materialized in the model's data dictionary at construction time so they are sent on the wire, while the attribute-access fallback for unset fields is preserved.

eng/emitters/pipelines/templates/stages/emitter-stages.yml

@@ -120,21 +120,6 @@ stages:
     variables:
       selfRepositoryPath: $(Build.SourcesDirectory)
     jobs:
-      - template: /eng/emitters/pipelines/templates/jobs/build-job.yml
-        parameters:
-          BuildPrereleaseVersion: ${{ parameters.BuildPrereleaseVersion }}
-          UseTypeSpecNext: ${{ parameters.UseTypeSpecNext }}
-          Publish: ${{ parameters.Publish }}
-          AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}
-          Packages: ${{ parameters.Packages }}
-          PackagePath: ${{ parameters.PackagePath }}
-          LanguageShortName: ${{ parameters.LanguageShortName }}
-          BuildArtifactName: build_artifacts_${{ parameters.LanguageShortName }}
-          NodeVersion: 20.x
-          Os: linux
-          EmitArtifacts: true # Emit artifacts only for the first job
-          PythonVersion: ${{ parameters.PythonVersion }}
-          RunSDLTools: true
       - template: /eng/emitters/pipelines/templates/jobs/build-job.yml
         parameters:
           BuildPrereleaseVersion: ${{ parameters.BuildPrereleaseVersion }}
@@ -147,18 +132,6 @@ stages:
           NodeVersion: 22.x
           Os: linux
           PythonVersion: ${{ parameters.PythonVersion }}
-      - template: /eng/emitters/pipelines/templates/jobs/build-job.yml
-        parameters:
-          BuildPrereleaseVersion: ${{ parameters.BuildPrereleaseVersion }}
-          UseTypeSpecNext: ${{ parameters.UseTypeSpecNext }}
-          Publish: ${{ parameters.Publish }}
-          AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}
-          Packages: ${{ parameters.Packages }}
-          PackagePath: ${{ parameters.PackagePath }}
-          LanguageShortName: ${{ parameters.LanguageShortName }}
-          NodeVersion: 20.x
-          Os: windows
-          PythonVersion: ${{ parameters.PythonVersion }}
       - template: /eng/emitters/pipelines/templates/jobs/build-job.yml
         parameters:
           BuildPrereleaseVersion: ${{ parameters.BuildPrereleaseVersion }}
@@ -197,20 +170,6 @@ stages:
           buildArtifactsPath: $(Pipeline.Workspace)/build_artifacts_${{ parameters.LanguageShortName }}
         jobs:
           - ${{ if parameters.UnitTestArgs }}:
-              - template: /eng/emitters/pipelines/templates/jobs/test-job.yml
-                parameters:
-                  AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}
-                  PackagePath: ${{ parameters.PackagePath }}
-                  TestArgs: ${{ parameters.UnitTestArgs }}
-                  LanguageShortName: ${{ parameters.LanguageShortName }}
-                  BuildArtifactName: build_artifacts_${{ parameters.LanguageShortName }}
-                  NodeVersion: 20.x
-                  Os: linux
-                  EmitArtifacts: true # Emit artifacts only for the first job
-                  CadlRanchName: ${{ parameters.CadlRanchName }} # only needed for first job
-                  EnableCadlRanchReport: ${{ parameters.EnableCadlRanchReport }}
-                  PythonVersion: ${{ parameters.PythonVersion }}
-                  UseTypeSpecNext: ${{ parameters.UseTypeSpecNext }}
               - template: /eng/emitters/pipelines/templates/jobs/test-job.yml
                 parameters:
                   AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}
@@ -222,17 +181,6 @@ stages:
                   Os: linux
                   PythonVersion: ${{ parameters.PythonVersion }}
                   UseTypeSpecNext: ${{ parameters.UseTypeSpecNext }}
-              - template: /eng/emitters/pipelines/templates/jobs/test-job.yml
-                parameters:
-                  AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}
-                  PackagePath: ${{ parameters.PackagePath }}
-                  TestArgs: ${{ parameters.UnitTestArgs }}
-                  LanguageShortName: ${{ parameters.LanguageShortName }}
-                  BuildArtifactName: build_artifacts_${{ parameters.LanguageShortName }}
-                  NodeVersion: 20.x
-                  Os: windows
-                  PythonVersion: ${{ parameters.PythonVersion }}
-                  UseTypeSpecNext: ${{ parameters.UseTypeSpecNext }}
               - template: /eng/emitters/pipelines/templates/jobs/test-job.yml
                 parameters:
                   AdditionalInitializeSteps: ${{ parameters.AdditionalInitializeSteps }}

eng/emitters/pipelines/templates/steps/test-step.yml

@@ -13,7 +13,7 @@ parameters:
   # Node version
   - name: NodeVersion
     type: string
-    default: "20.x"
+    default: "22.x"
 
   # Arguments needed to run tests
   - name: TestArgs

packages/http-client-python/generator/pygen/codegen/templates/model_base.py.jinja2

@@ -642,6 +642,14 @@ class Model(_MyMutableMapping):
                     if v is not None
                 }
             )
+        # Apply client default values for fields the caller didn't set so that
+        # defaults are part of `_data` and therefore included during serialization.
+        for rf in self._attr_to_rest_field.values():
+            if rf._default is _UNSET:
+                continue
+            if rf._rest_name in dict_to_pass:
+                continue
+            dict_to_pass[rf._rest_name] = _create_value(rf, rf._default)
         super().__init__(dict_to_pass)
 
     def _init_from_xml(self, element: ET.Element) -> dict[str, typing.Any]:

packages/http-client-python/package.json

@@ -103,7 +103,7 @@
     "@azure-tools/typespec-azure-resource-manager": "~0.67.0",
     "@azure-tools/typespec-azure-rulesets": "~0.67.0",
     "@azure-tools/typespec-client-generator-core": "~0.67.0",
-    "@azure-tools/azure-http-specs": "0.1.0-alpha.39",
+    "@azure-tools/azure-http-specs": "0.1.0-alpha.40-dev.12",
     "@typespec/compiler": "^1.11.0",
     "@typespec/http": "^1.11.0",
     "@typespec/openapi": "^1.11.0",