code: def get_cycle_mrkr(self, end=False):
          
          if self.annot is None:  # remove if buttons are disabled
              self.parent.statusBar().showMessage('No score file loaded')
              return
  
          window_start = self.parent.value('window_start')
          window_length = self.parent.value('window_length')
  
          try:
              self.annot.set_cycle_mrkr(window_start, end=end)
  
          except KeyError:
              msg = ('The start of the window does not correspond to any epoch '
                     'in sleep scoring file')
              self.parent.statusBar().showMessage(msg)
              lg.debug(msg)
  
          else:
              bound = 'start'
              if end:
                  bound = 'end'
              lg.info('User marked ' + str(window_start) + ' as cycle ' +
                      bound)
  
              self.parent.overview.mark_cycles(window_start, window_length,
                                               end=end)
docs: Mark cycle start or end.
  
          Parameters
          ----------
          end : bool
              If True, marks a cycle end; otherwise, it's a cycle start