Class Failure

returns/result.py:347–407

Represents a calculation which has failed. It should contain an error code or message.

@final  # noqa: WPS338
class Failure(Result[Any, _ErrorType_co]):  # noqa: WPS338
    """
    Represents a calculation which has failed.

    It should contain an error code or message.
    """

    __slots__ = ()

    _inner_value: _ErrorType_co

    def __init__(self, inner_value: _ErrorType_co) -> None:
        """Failure constructor."""
        super().__init__(inner_value)
        object.__setattr__(self, '_trace', self._get_trace())

    if not TYPE_CHECKING:  # noqa: WPS604  # pragma: no branch

        def alt(self, function):
            """Composes failed container with a pure function to modify failure."""  # noqa: E501
            return Failure(function(self._inner_value))

        def map(self, function):
            """Does nothing for ``Failure``."""
            return self

        def bind(self, function):
            """Does nothing for ``Failure``."""
            return self

        #: Alias for `bind` method. Part of the `ResultBasedN` interface.
        bind_result = bind

        def lash(self, function):
            """Composes this container with a function returning container."""
            return function(self._inner_value)

        def apply(self, container):
            """Does nothing for ``Failure``."""
            return self

        def value_or(self, default_value):
            """Returns default value for failed container."""
            return default_value

    def swap(self):
        """Failures swap to :class:`Success`."""
        return Success(self._inner_value)

    def unwrap(self) -> Never:
        """Raises an exception, since it does not have a value inside."""
        if isinstance(self._inner_value, Exception):
            raise UnwrapFailedError(self) from self._inner_value
        raise UnwrapFailedError(self)

    def failure(self) -> _ErrorType_co:
        """Returns failed value."""
        return self._inner_value