Class Instance

traitlets/traitlets.py:2192–2349

A trait whose value must be an instance of a specified class. The value can also be an instance of a subclass of the specified class. Subclasses can declare default classes by overriding the klass attribute

class Instance(ClassBasedTraitType[T, T]):
    """A trait whose value must be an instance of a specified class.

    The value can also be an instance of a subclass of the specified class.

    Subclasses can declare default classes by overriding the klass attribute
    """

    klass: str | type[T] | None = None

    if t.TYPE_CHECKING:

        @t.overload
        def __init__(
            self: Instance[T],
            klass: type[T] = ...,
            args: tuple[t.Any, ...] | None = ...,
            kw: dict[str, t.Any] | None = ...,
            allow_none: Literal[False] = ...,
            read_only: bool | None = ...,
            help: str | None = ...,
            **kwargs: t.Any,
        ) -> None:
            ...

        @t.overload
        def __init__(
            self: Instance[T | None],
            klass: type[T] = ...,
            args: tuple[t.Any, ...] | None = ...,
            kw: dict[str, t.Any] | None = ...,
            allow_none: Literal[True] = ...,
            read_only: bool | None = ...,
            help: str | None = ...,
            **kwargs: t.Any,
        ) -> None:
            ...

        @t.overload
        def __init__(
            self: Instance[t.Any],
            klass: str | None = ...,
            args: tuple[t.Any, ...] | None = ...,
            kw: dict[str, t.Any] | None = ...,
            allow_none: Literal[False] = ...,
            read_only: bool | None = ...,
            help: str | None = ...,
            **kwargs: t.Any,
        ) -> None:
            ...

        @t.overload
        def __init__(
            self: Instance[t.Any | None],
            klass: str | None = ...,
            args: tuple[t.Any, ...] | None = ...,
            kw: dict[str, t.Any] | None = ...,
            allow_none: Literal[True] = ...,