tz.py 文件源码

def _isdst(self, dt, fold_naive=True):
        # We can't use mktime here. It is unstable when deciding if
        # the hour near to a change is DST or not.
        #
        # timestamp = time.mktime((dt.year, dt.month, dt.day, dt.hour,
        #                         dt.minute, dt.second, dt.weekday(), 0, -1))
        # return time.localtime(timestamp).tm_isdst
        #
        # The code above yields the following result:
        #
        # >>> import tz, datetime
        # >>> t = tz.tzlocal()
        # >>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        # 'BRDT'
        # >>> datetime.datetime(2003,2,16,0,tzinfo=t).tzname()
        # 'BRST'
        # >>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        # 'BRST'
        # >>> datetime.datetime(2003,2,15,22,tzinfo=t).tzname()
        # 'BRDT'
        # >>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        # 'BRDT'
        #
        # Here is a more stable implementation:
        #
        if not self._hasdst:
            return False

        # Check for ambiguous times:
        dstval = self._naive_is_dst(dt)
        fold = getattr(dt, 'fold', None)

        if self.is_ambiguous(dt):
            if fold is not None:
                return not self._fold(dt)
            else:
                return True

        return dstval