code: def add_nevents(self, experiment_summ_id, num_events, add_to_current = True):
  		
  		for row in self:
  			if row.experiment_summ_id != experiment_summ_id:
  				continue
  			if row.nevents is None:
  				row.nevents = 0
  			if add_to_current:
  				row.nevents += num_events
  				return row.nevents
  			else:
  				row.nevents = num_events
  				return row.nevents
  				
  		# if get to here, couldn't find experiment_summ_id in the table
  		raise ValueError("'%s' could not be found in the table" % (str(experiment_summ_id)))
docs: Add num_events to the nevents column in a specific entry in the table. If
  		add_to_current is set to False, will overwrite the current nevents entry in
  		the row with num_events. Otherwise, default is to add num_events to
  		the current value.
  
  		Note: Can subtract events by passing a negative number to num_events.