Class TestTimezoneConversions

Lib/test/datetimetester.py:5825–6078

utc_fake = FixedOffset(-12*60, "UTCfake", 0)

class TestTimezoneConversions(unittest.TestCase):
    # The DST switch times for 2002, in std time.
    dston = datetime(2002, 4, 7, 2)
    dstoff = datetime(2002, 10, 27, 1)

    theclass = datetime

    # Check a time that's inside DST.
    def checkinside(self, dt, tz, utc, dston, dstoff):
        self.assertEqual(dt.dst(), HOUR)

        # Conversion to our own timezone is always an identity.
        self.assertEqual(dt.astimezone(tz), dt)

        asutc = dt.astimezone(utc)
        there_and_back = asutc.astimezone(tz)

        # Conversion to UTC and back isn't always an identity here,
        # because there are redundant spellings (in local time) of
        # UTC time when DST begins:  the clock jumps from 1:59:59
        # to 3:00:00, and a local time of 2:MM:SS doesn't really
        # make sense then.  The classes above treat 2:MM:SS as
        # daylight time then (it's "after 2am"), really an alias
        # for 1:MM:SS standard time.  The latter form is what
        # conversion back from UTC produces.
        if dt.date() == dston.date() and dt.hour == 2:
            # We're in the redundant hour, and coming back from
            # UTC gives the 1:MM:SS standard-time spelling.
            self.assertEqual(there_and_back + HOUR, dt)
            # Although during was considered to be in daylight
            # time, there_and_back is not.
            self.assertEqual(there_and_back.dst(), ZERO)
            # They're the same times in UTC.
            self.assertEqual(there_and_back.astimezone(utc),
                             dt.astimezone(utc))
        else:
            # We're not in the redundant hour.
            self.assertEqual(dt, there_and_back)

        # Because we have a redundant spelling when DST begins, there is
        # (unfortunately) an hour when DST ends that can't be spelled at all in
        # local time.  When DST ends, the clock jumps from 1:59 back to 1:00
        # again.  The hour 1:MM DST has no spelling then:  1:MM is taken to be
        # standard time.  1:MM DST == 0:MM EST, but 0:MM is taken to be
        # daylight time.  The hour 1:MM daylight == 0:MM standard can't be
        # expressed in local time.  Nevertheless, we want conversion back
        # from UTC to mimic the local clock's "repeat an hour" behavior.
        nexthour_utc = asutc + HOUR
        nexthour_tz = nexthour_utc.astimezone(tz)
        if dt.date() == dstoff.date() and dt.hour == 0:
            # We're in the hour before the last DST hour.  The last DST hour
            # is ineffable.  We want the conversion back to repeat 1:MM.
            self.assertEqual(nexthour_tz, dt.replace(hour=1))
            nexthour_utc += HOUR
            nexthour_tz = nexthour_utc.astimezone(tz)
            self.assertEqual(nexthour_tz, dt.replace(hour=1))
        else:
            self.assertEqual(nexthour_tz - dt, HOUR)