log an event
        
        Parameters
        ----------
        event : string
        evresult : string
        note : string

def _log_an_event(self, event, evresult='No Result', note='No Note'):
        """ log an event
        
        Parameters
        ----------
        event : string
        evresult : string
        note : string
        """
        objs = object_session(self)
        evnt = SymbolLogEvent(event, evresult, note, sym=self.name)
        objs.add(evnt)
        objs.commit()