Class Enum

traitlets/traitlets.py:3188–3274

An enum whose value must be in a given sequence.

class Enum(TraitType[G, G]):
    """An enum whose value must be in a given sequence."""

    if t.TYPE_CHECKING:

        @t.overload
        def __init__(
            self: Enum[G],
            values: t.Sequence[G],
            default_value: G | Sentinel = ...,
            allow_none: Literal[False] = ...,
            read_only: bool | None = ...,
            help: str | None = ...,
            config: t.Any = ...,
            **kwargs: t.Any,
        ) -> None:
            ...

        @t.overload
        def __init__(
            self: Enum[G | None],
            values: t.Sequence[G] | None,
            default_value: G | Sentinel | None = ...,
            allow_none: Literal[True] = ...,
            read_only: bool | None = ...,
            help: str | None = ...,
            config: t.Any = ...,
            **kwargs: t.Any,
        ) -> None:
            ...

    def __init__(
        self: Enum[G],
        values: t.Sequence[G] | None,
        default_value: G | Sentinel | None = Undefined,
        allow_none: bool = False,
        read_only: bool | None = None,
        help: str | None = None,
        config: t.Any = None,
        **kwargs: t.Any,
    ) -> None:
        self.values = values
        if allow_none is True and default_value is Undefined:
            default_value = None
        kwargs["allow_none"] = allow_none
        kwargs["read_only"] = read_only
        kwargs["help"] = help
        kwargs["config"] = config
        super().__init__(default_value, **kwargs)

    def validate(self, obj: t.Any, value: t.Any) -> G:
        if self.values and value in self.values:
            return value  # type:ignore[no-any-return]
        self.error(obj, value)

    def _choices_str(self, as_rst: bool = False) -> str:
        """Returns a description of the trait choices (not none)."""
        choices = self.values or []