streamlit/streamlit · error · ValueError

Expected an EnumMeta/Type in the second argument. Got {type(

Error message

Expected an EnumMeta/Type in the second argument. Got {type(to_enum_class)}

What it means

Error "Expected an EnumMeta/Type in the second argument. Got {type(to_enum_class)}" thrown in streamlit/streamlit.

Source

Thrown at lib/streamlit/elements/lib/options_selector_utils.py:162

E1 = TypeVar("E1", bound=Enum)
E2 = TypeVar("E2", bound=Enum)

_ALLOWED_ENUM_COERCION_CONFIG_SETTINGS = ("off", "nameOnly", "nameAndValue")


def _coerce_enum(from_enum_value: E1, to_enum_class: type[E2]) -> E1 | E2:
    """Attempt to coerce an Enum value to another EnumMeta.

    An Enum value of EnumMeta E1 is considered coercible to EnumType E2
    if the EnumMeta __qualname__ match and the names of their members
    match as well. (This is configurable in streamlist configs)
    """
    if not isinstance(from_enum_value, Enum):
        raise ValueError(  # noqa: TRY004
            f"Expected an Enum in the first argument. Got {type(from_enum_value)}"
        )
    if not isinstance(to_enum_class, EnumMeta):
        raise ValueError(  # noqa: TRY004
            f"Expected an EnumMeta/Type in the second argument. Got {type(to_enum_class)}"
        )
    if isinstance(from_enum_value, to_enum_class):
        return from_enum_value  # Enum is already a member, no coercion necessary

    coercion_type = config.get_option("runner.enumCoercion")
    if coercion_type not in _ALLOWED_ENUM_COERCION_CONFIG_SETTINGS:
        raise StreamlitValueError(
            "runner.enumCoercion",
            [f"'{v}'" for v in _ALLOWED_ENUM_COERCION_CONFIG_SETTINGS],
        )
    if coercion_type == "off":
        return from_enum_value  # do not attempt to coerce

    # We now know this is an Enum AND the user has configured coercion enabled.
    # Check if we do NOT meet the required conditions and log a failure message
    # if that is the case.
    from_enum_class = from_enum_value.__class__

View on GitHub (pinned to 202661fc55)

When it happens

Trigger: Thrown at lib/streamlit/elements/lib/options_selector_utils.py:162 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of streamlit/streamlit@202661fc55 (2026-08-26). Data as JSON: /api/errors/53c5b7753886fc9e. Report an issue: GitHub.