def off(self, event, cb):
        if self._observers not in event:
            raise KeyError(
                "No observers are registered for the event: ",
                event)
        else:
            if cb not in self._observers[event]:
                raise ValueError(
                    "Observer is not registered for the event: ",
                    event)
            else:
                self._observers[event].remove(cb)
dataset/ETHPy150Open theycallmeswift/BreakfastSerial/BreakfastSerial/util.py/EventEmitter.off/swapped operands of `not in`