code: def deleteObserver(self, observer):
          
          Observable.deleteObserver(self, observer)
          # If self.startOnDemand is True, the reader monitoring
          # thread is stopped when there are no more observers.
          if self.startOnDemand:
              if 0 == self.countObservers():
                  self.rmthread.stop()
                  del self.rmthread
                  self.rmthread = None
docs: Remove an observer.