Simple TZ implementation

p_data.py

from datetime import datetime, tzinfo, timedelta

class TZOffset(tzinfo):
    def __init__(self, offset=0, *args, **kwds):
        self.gmt_offset = offset
        super(TZOffset, self).__init__(*args, **kwds)
    def utcoffset(self, dt):
        return timedelta(hours=self.gmt_offset) + self.dst(dt)
    def tzname(self,dt):
        return "GMT %s%s" % (('+' if self.gmt_offset > 0 else ''), self.gmt_offset)
    def dst(self,dt):
        d = datetime(dt.year, 4, 1)
        self.dston = d - timedelta(days=d.weekday() + 1)
        d = datetime(dt.year, 11, 1)
        self.dstoff = d - timedelta(days=d.weekday() + 1)
        if self.dston <=  dt.replace(tzinfo=None) < self.dstoff:
            return timedelta(hours=1)
        else:
            return timedelta(0)

def as_time_zone(dt, tz):
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=TZOffset(0))
    if dt.tzinfo is tz:
        return dt
    utc = (dt - dt.utcoffset()).replace(tzinfo=tz)
    return tz.fromutc(utc)

now = datetime.now()
now_gmt_1 = datetime.now(TZOffset(1))
tz_1 = TZOffset(0)
tz_2 = TZOffset(-12)
tz_3 = TZOffset(2)

now_tz_aware = now.replace(tzinfo=tz_1)
now_with_new_tz = as_time_zone(now_tz_aware, tz_2)
now_with_new_tz_2 = as_time_zone(now_with_new_tz, tz_3)

dt1 = datetime(2014, 12, 24, 16, 30, tzinfo=tz_1)
dt2 = dt1.replace(month=06)

print 'Date \t \t \t  \t \t', 'Timezone'
print now, ' \t \t', now.tzname()
print now_gmt_1, '\t', now_gmt_1.tzname()
print now_with_new_tz, '\t', now_with_new_tz.tzname()
print now_with_new_tz_2, '\t', now_with_new_tz_2.tzname()
print 'Daylight Savings'
print 'Wintertime', dt1.utctimetuple()
print 'Summertime', dt2.utctimetuple()