code: def add_handler(  # noqa: F811
          self, fd: Union[int, _Selectable], handler: Callable[..., None], events: int
      ) -> None:
          
          raise NotImplementedError()
docs: Registers the given handler to receive the given events for ``fd``.
  
          The ``fd`` argument may either be an integer file descriptor or
          a file-like object with a ``fileno()`` and ``close()`` method.
  
          The ``events`` argument is a bitwise or of the constants
          ``IOLoop.READ``, ``IOLoop.WRITE``, and ``IOLoop.ERROR``.
  
          When an event occurs, ``handler(fd, events)`` will be run.
  
          .. versionchanged:: 4.0
             Added the ability to pass file-like objects in addition to
             raw file descriptors.