Class UninhabitedType

mypy/types.py:1374–1426

This type has no members. This type is the bottom type. With strict Optional checking, it is the only common subtype between all other types, which allows `meet` to be well defined. Without strict Optional checking, NoneType fills this role. In general, for any type T:

class UninhabitedType(ProperType):
    """This type has no members.

    This type is the bottom type.
    With strict Optional checking, it is the only common subtype between all
    other types, which allows `meet` to be well defined.  Without strict
    Optional checking, NoneType fills this role.

    In general, for any type T:
        join(UninhabitedType, T) = T
        meet(UninhabitedType, T) = UninhabitedType
        is_subtype(UninhabitedType, T) = True
    """

    __slots__ = ("ambiguous",)

    ambiguous: bool  # Is this a result of inference for a variable without constraints?

    def __init__(self, line: int = -1, column: int = -1) -> None:
        super().__init__(line, column)
        self.ambiguous = False

    def can_be_true_default(self) -> bool:
        return False

    def can_be_false_default(self) -> bool:
        return False

    def accept(self, visitor: TypeVisitor[T]) -> T:
        return visitor.visit_uninhabited_type(self)

    def __hash__(self) -> int:
        return hash((UninhabitedType, self.ambiguous))

    def __eq__(self, other: object) -> bool:
        return isinstance(other, UninhabitedType) and other.ambiguous == self.ambiguous

    def serialize(self) -> JsonDict:
        return {".class": "UninhabitedType"}

    @classmethod
    def deserialize(cls, data: JsonDict) -> UninhabitedType:
        assert data[".class"] == "UninhabitedType"
        return UninhabitedType()

    def write(self, data: WriteBuffer) -> None:
        write_tag(data, UNINHABITED_TYPE)
        write_tag(data, END_TAG)

    @classmethod
    def read(cls, data: ReadBuffer) -> UninhabitedType:
        assert read_tag(data) == END_TAG
        return UninhabitedType()


class NoneType(ProperType):