code: def confdate(self):
          
          date = self._confevent.get('confdate', {})
          if len(date) > 0:
              start = {k: int(v) for k, v in date['startdate'].items()}
              end = {k: int(v) for k, v in date['enddate'].items()}
              return ((start['@year'], start['@month'], start['@day']),
                      (end['@year'], end['@month'], end['@day']))
          else:
              return ((None, None, None), (None, None, None))
docs: Date range of the conference the abstract belongs to represented
          by two tuples in the form (YYYY, MM, DD).