Python: fix(python): preserve Pydantic field descriptions in schemas

python/semantic_kernel/schema/kernel_json_schema_builder.py

@@ -89,12 +89,19 @@ def build_model_schema(
             field_description = None
             if hasattr(model, "model_fields") and field_name in model.model_fields:
                 field_info = model.model_fields[field_name]
-                if isinstance(field_info.metadata, dict):
-                    field_description = field_info.metadata.get("description")
-                elif isinstance(field_info.metadata, list) and field_info.metadata:
-                    field_description = field_info.metadata[0]
-                elif hasattr(field_info, "description"):
-                    field_description = field_info.description
+                field_description = getattr(field_info, "description", None)
+                if field_description is None:
+                    metadata = getattr(field_info, "metadata", None)
+                    if isinstance(metadata, dict):
+                        field_description = metadata.get("description")
+                    elif isinstance(metadata, (list, tuple)):
+                        for item in metadata:
+                            if isinstance(item, str):
+                                field_description = item
+                                break
+                            if isinstance(item, dict) and isinstance(item.get("description"), str):
+                                field_description = item["description"]
+                                break
             if not cls._is_optional(field_type):
                 required.append(field_name)
             properties[field_name] = cls.build(field_type, field_description, structured_output)

python/tests/unit/schema/test_schema_builder.py

@@ -6,6 +6,7 @@
 from unittest.mock import Mock
 
 import pytest
+from pydantic import Field
 
 from semantic_kernel.connectors.utils.structured_output_schema import generate_structured_output_response_format_schema
 from semantic_kernel.kernel_pydantic import KernelBaseModel
@@ -76,6 +77,14 @@ class PydanticReasoning(KernelBaseModel):
     final_answer: str
 
 
+class PydanticModelWithConstrainedField(KernelBaseModel):
+    top_p: float = Field(default=0.9, ge=0.0, le=1.0, description="nucleus sampling")
+
+
+class PydanticModelWithAnnotatedDescription(KernelBaseModel):
+    name: Annotated[str, "display name"]
+
+
 class NonPydanticStep:
     explanation: str
     output: str
@@ -156,6 +165,20 @@ def test_build_model_schema():
     assert result == expected_schema
 
 
+def test_build_model_schema_uses_pydantic_description_with_constraints():
+    schema = KernelJsonSchemaBuilder.build_model_schema(PydanticModelWithConstrainedField)
+
+    assert schema["properties"]["top_p"] == {"type": "number", "description": "nucleus sampling"}
+    json.dumps(schema)
+
+
+def test_build_model_schema_uses_annotated_metadata_description():
+    schema = KernelJsonSchemaBuilder.build_model_schema(PydanticModelWithAnnotatedDescription)
+
+    assert schema["properties"]["name"] == {"type": "string", "description": "display name"}
+    json.dumps(schema)
+
+
 def test_build_from_type_name():
     expected_schema = {"type": "string", "description": "A simple string"}
     result = KernelJsonSchemaBuilder.build_from_type_name("str", description="A simple string")