How to use the stacker.status.FailedStatus function in stacker

class DidNotChangeStatus(SkippedStatus):
    reason = "nochange"


class StackDoesNotExist(SkippedStatus):
    reason = "does not exist in cloudformation"


PENDING = PendingStatus()
WAITING = PendingStatus(reason="waiting")
SUBMITTED = SubmittedStatus()
COMPLETE = CompleteStatus()
SKIPPED = SkippedStatus()
FAILED = FailedStatus()
INTERRUPTED = FailedStatus(reason="interrupted")

return old_status
            elif provider.is_stack_destroyed(provider_stack):
                logger.debug("Stack %s finished deleting", stack.fqn)
                recreate = True
                # Continue with creation afterwards
            # Failure must be checked *before* completion, as both will be true
            # when completing a rollback, and we don't want to consider it as
            # a successful update.
            elif provider.is_stack_failed(provider_stack):
                reason = old_status.reason
                if 'rolling' in reason:
                    reason = reason.replace('rolling', 'rolled')
                status_reason = provider.get_rollback_status_reason(stack.fqn)
                logger.info(
                    "%s Stack Roll Back Reason: " + status_reason, stack.fqn)
                return FailedStatus(reason)

            elif provider.is_stack_completed(provider_stack):
                stack.set_outputs(
                    provider.get_output_dict(provider_stack))
                return CompleteStatus(old_status.reason)
            else:
                return old_status

        logger.debug("Resolving stack %s", stack.fqn)
        stack.resolve(self.context, self.provider)

        logger.debug("Launching stack %s now.", stack.fqn)
        template = self._template(stack.blueprint)
        stack_policy = self._stack_policy(stack)
        tags = build_stack_tags(stack)
        parameters = self.build_parameters(stack, provider_stack)

def walk_func(step):
            # Before we execute the step, we need to ensure that it's
            # transitive dependencies are all in an "ok" state. If not, we
            # won't execute this step.
            for dep in self.graph.downstream(step.name):
                if not dep.ok:
                    step.set_status(FailedStatus("dependency has failed"))
                    return step.ok

            return step.run()

def _run_once(self):
        try:
            status = self.fn(self.stack, status=self.status)
        except Exception as e:
            logger.exception(e)
            status = FailedStatus(reason=str(e))
        self.set_status(status)
        return status

class DidNotChangeStatus(SkippedStatus):
    reason = "nochange"


class StackDoesNotExist(SkippedStatus):
    reason = "does not exist in cloudformation"


PENDING = PendingStatus()
WAITING = PendingStatus(reason="waiting")
SUBMITTED = SubmittedStatus()
COMPLETE = CompleteStatus()
SKIPPED = SkippedStatus()
FAILED = FailedStatus()
INTERRUPTED = FailedStatus(reason="interrupted")

def walk_func(step):
            # Before we execute the step, we need to ensure that it's
            # transitive dependencies are all in an "ok" state. If not, we
            # won't execute this step.
            for dep in self.graph.downstream(step.name):
                if not dep.ok:
                    step.set_status(FailedStatus("dependency has failed"))
                    return step.ok

            return step.run()

def __init__(self, reason=None):
        super(FailedStatus, self).__init__("failed", 4, reason)