code: def exceptions(self):
          
          ex = {}
          for sd in self.root.xpath('exceptions/exception'):
              bits = str(sd.text).split(' ')
              date = text_to_date(bits.pop(0))
              ex.setdefault(date, []).extend([
                  _time_text_to_period(t)
                  for t in bits
              ])
          return ex
docs: A dict of dates -> [Period time tuples] representing exceptions
          to the base recurrence pattern.