Class UseEnum

traitlets/traitlets.py:4211–4310

Use a Enum class as model for the data type description. Note that if no default-value is provided, the first enum-value is used as default-value. .. sourcecode:: python # -- SINCE: Python 3.4 (or install backport: pip install enum34) import enum from traitlets

class UseEnum(TraitType[t.Any, t.Any]):
    """Use a Enum class as model for the data type description.
    Note that if no default-value is provided, the first enum-value is used
    as default-value.

    .. sourcecode:: python

        # -- SINCE: Python 3.4 (or install backport: pip install enum34)
        import enum
        from traitlets import HasTraits, UseEnum


        class Color(enum.Enum):
            red = 1  # -- IMPLICIT: default_value
            blue = 2
            green = 3


        class MyEntity(HasTraits):
            color = UseEnum(Color, default_value=Color.blue)


        entity = MyEntity(color=Color.red)
        entity.color = Color.green  # USE: Enum-value (preferred)
        entity.color = "green"  # USE: name (as string)
        entity.color = "Color.green"  # USE: scoped-name (as string)
        entity.color = 3  # USE: number (as int)
        assert entity.color is Color.green
    """

    default_value: enum.Enum | None = None
    info_text = "Trait type adapter to a Enum class"

    def __init__(
        self, enum_class: type[t.Any], default_value: t.Any = None, **kwargs: t.Any
    ) -> None:
        assert issubclass(enum_class, enum.Enum), "REQUIRE: enum.Enum, but was: %r" % enum_class
        allow_none = kwargs.get("allow_none", False)
        if default_value is None and not allow_none:
            default_value = next(iter(enum_class.__members__.values()))
        super().__init__(default_value=default_value, **kwargs)
        self.enum_class = enum_class
        self.name_prefix = enum_class.__name__ + "."

    def select_by_number(self, value: int, default: t.Any = Undefined) -> t.Any:
        """Selects enum-value by using its number-constant."""
        assert isinstance(value, int)
        enum_members = self.enum_class.__members__
        for enum_item in enum_members.values():
            if enum_item.value == value:
                return enum_item
        # -- NOT FOUND:
        return default

    def select_by_name(self, value: str, default: t.Any = Undefined) -> t.Any:
        """Selects enum-value by using its name or scoped-name."""
        assert isinstance(value, str)
        if value.startswith(self.name_prefix):