def transitions(self, year):
if not self.hasdst:<EOL><INDENT>return None<EOL><DEDENT>base_year = datetime.datetime(year, <NUM_LIT:1>, <NUM_LIT:1>)<EOL>start = base_year + self._start_delta<EOL>end = base_year + self._end_delta<EOL>return (start, end)<EOL>
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.