fix(python): serialize Pydantic models with mode='json' in tool results - #2225
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SteveSandersonMS merged 2 commits intoAug 3, 2026
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model_dump() defaults to mode='python', which leaves datetime, UUID, Decimal, Enum and set as native Python objects. json.dumps then fails on these, and the error is swallowed as a generic tool failure. Use model_dump(mode='json') so Pydantic converts all fields to JSON-safe types before serialization. Closes github#2203
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@SteveSandersonMS One-line Python fix + test. Tool results with datetime/UUID/Decimal/Enum were silently failing because model_dump() defaults to mode='python'. Tests pass. |
Assert the JSON representation of date and datetime fields, cover set serialization, and fix import ordering for Ruff. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Fix Python tool handlers returning Pydantic models containing
datetime,date,UUID,Decimal,Enum, orsetfields being silently reported as failures.Root cause
BaseModel.model_dump()defaults tomode="python", which keeps native Python types.json.dumpsthen fails on those values, and the error is surfaced as a generic tool failure.Fix
Use
model_dump(mode="json")so Pydantic converts model fields to JSON-safe values beforejson.dumpsruns.Test
Added
test_pydantic_model_with_non_primitive_fields_is_serialized, covering the exact JSON representations of UUID, datetime, date, Decimal, Enum, and set fields.This addresses the Pydantic-model case in #2203. Plain dictionaries containing native non-JSON types remain outside this focused change.