code: def cancel(
              self,
              identifier: typing.Any,
              exc_type: typing.Optional[type]=None,
      ) -> bool:
          
          raise NotImplementedError()
docs: Cancel an active coroutine and remove it from the schedule.
  
          Args:
              identifier (typing.Any): The identifier returned from add.
              exc_type (typing.Optional[type]): The exception type to throw into
                  the coroutine on cancel. No exception is thrown if nothing is
                  given. Instead the coroutine is no longer processed.
  
          Returns:
              bool: True if the coroutine is cancelled. False if the identifier
                  is invalid or if the coroutine is complete.