code: def set_exception(self, exception):
          '''
          Set an exception to Future object, wake up all the waiters
          
          :param exception: exception to set
          '''
          if hasattr(self, '_result'):
              raise ValueError('Cannot set the result twice')
          self._result = None
          self._exception = exception
          self._scheduler.emergesend(FutureEvent(self, exception = exception)f set_exception(self, exception):
          '''
          Set an exception to Future object, wake up all the waiters
          
          :param exception: exception to set
          '''
          if hasattr(self, '_result'):
              raise ValueError('Cannot set the result twice')
          self._result = None
          self._exception = exception
          self._scheduler.emergesend(FutureEvent(self, exception = exception))
docs: Set an exception to Future object, wake up all the waiters
          
          :param exception: exception to set