fix(output): render Enum members as str in JSON serializer

[kirangadhave]

Summary

Plain enum.Enum members displayed in mo.ui.table or as a pandas DataFrame rendered their __dict__ internals (_value_, _name_, __objclass__, _sort_order_) instead of a readable label.

The table/DataFrame path serializes cells through sanitize_json_bigint, which uses stdlib json.dumps. stdlib json has no native Enum support, so members reached the generic __dict__ fallback in enc_hook and leaked their internals. The msgspec-native encode_json_str path was unaffected because msgspec encodes Enum natively (as .value).

This adds an explicit enum.Enum branch in enc_hook ahead of the __dict__/__slots__ fallbacks that returns str(obj) (e.g. "TestEnum.ONE"). IntEnum and StrEnum still match their int/str isinstance branches first, so the existing test (encode_json_str(Color.RED) == "1") is preserved.

Fixes #9576

Test plan

• make py-check
• pytest tests/_plugins/core/test_json_encoder.py -k enum (3 passed, including new test_enum_via_sanitize_json_bigint)
• Manual repro from the bug report — mo.ui.table and pd.DataFrame views show TestEnum.ONE / TestEnum.TWO in the Enum column

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	May 18, 2026 11:58pm

[kirangadhave]

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[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant UI as mo.ui.table / DataFrame
    participant Sanitize as sanitize_json_bigint()
    participant JSONLib as stdlib json.dumps
    participant EncHook as enc_hook()
    participant EnumMember as Enum Member (e.g. TestEnum.ONE)
    participant Fallback as __dict__ / __slots__ fallback

    Note over UI,Sanitize: Table serialization path
    UI->>Sanitize: serialize cell values
    Sanitize->>JSONLib: json.dumps() with enc_hook
    JSONLib->>EncHook: call enc_hook(obj)
    EncHook->>EnumMember: isinstance(obj, enum.Enum)?
    alt Is Enum
        EncHook-->>JSONLib: return str(obj) (e.g. "TestEnum.ONE")
    else Not Enum
        EncHook->>Fallback: check __dict__ / __slots__
        Fallback-->>JSONLib: return dict/list
    end
    JSONLib-->>Sanitize: JSON string
    Sanitize-->>UI: rendered cell values

    Note over UI,Sanitize: msgspec path (unaffected)
    alt IntEnum member (e.g. Color.RED)
        EncHook->>EnumMember: isinstance(obj, int)?
        EncHook-->>JSONLib: return obj.value (e.g. 1)
    else StrEnum member
        EncHook->>EnumMember: isinstance(obj, str)?
        EncHook-->>JSONLib: return obj.value
    end

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[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant UI as mo.ui.table / DataFrame
    participant Sanitize as sanitize_json_bigint()
    participant JSONLib as stdlib json.dumps
    participant EncHook as enc_hook()
    participant EnumMember as Enum Member (e.g. TestEnum.ONE)
    participant Fallback as __dict__ / __slots__ fallback

    Note over UI,Sanitize: Table serialization path
    UI->>Sanitize: serialize cell values
    Sanitize->>JSONLib: json.dumps() with enc_hook
    JSONLib->>EncHook: call enc_hook(obj)
    EncHook->>EnumMember: isinstance(obj, enum.Enum)?
    alt Is Enum
        EncHook-->>JSONLib: return str(obj) (e.g. "TestEnum.ONE")
    else Not Enum
        EncHook->>Fallback: check __dict__ / __slots__
        Fallback-->>JSONLib: return dict/list
    end
    JSONLib-->>Sanitize: JSON string
    Sanitize-->>UI: rendered cell values

    Note over UI,Sanitize: msgspec path (unaffected)
    alt IntEnum member (e.g. Color.RED)
        EncHook->>EnumMember: isinstance(obj, int)?
        EncHook-->>JSONLib: return obj.value (e.g. 1)
    else StrEnum member
        EncHook->>EnumMember: isinstance(obj, str)?
        EncHook-->>JSONLib: return obj.value
    end

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🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.23.7-dev47