code: def transitions(self, year):
          
          if not self.hasdst:
              return None
  
          base_year = datetime.datetime(year, 1, 1)
  
          start = base_year + self._start_delta
          end = base_year + self._end_delta
  
          return (start, end)
docs: For a given year, get the DST on and off transition times, expressed
          always on the standard time side. For zones with no transitions, this
          function returns ``None``.
  
          :param year:
              The year whose transitions you would like to query.
  
          :return:
              Returns a :class:`tuple` of :class:`datetime.datetime` objects,
              ``(dston, dstoff)`` for zones with an annual DST transition, or
              ``None`` for fixed offset zones.