[python] Fix @clientDefaultValue serialization regression from #10476

[Copilot]

Follow-up to #10476 addressing review comment r3160211783.

#10476 stopped pre-populating Model._data with @clientDefaultValue defaults in __init__ and instead added a fallback in _RestField.__get__. That fallback only covers Python attribute reads — serialization goes through dict(model.items()), which iterates _data, so client defaults were silently dropped from request bodies.

Repro against azure-client-generator-core/client-default-value:

body = ModelWithDefaultValues(name="test")
client.put_model_property(body=body)
# Sent:     {"name": "test"}
# Expected: {"name": "test", "timeout": 30, "tier": "standard", "retry": true}

Changes

• generator/pygen/codegen/templates/model_base.py.jinja2: After dict_to_pass is populated from args/kwargs in Model.__init__, fill in _default for any rest field the caller didn't provide. Restores pre-[python] add support for clientDefaultValue to unblock CI #10476 wire behavior while keeping the new _RestField.__get__ fallback as a safety net for unset fields without a default.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-python@10546

commit: a477100

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-client-python

Show changes

@typespec/http-client-python - fix ✏️

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.

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension