local timezone class

tzl.py

# A local timezone class that inherits its behavior from the time
# module's knowledge about the local time zone.

# TODO: Use tm_gmtoff and tm_zone if supported?  (Probably should be a
# separate class so we can compare them.)

import calendar  # TODO: Really shouldn't.
import datetime
import time


class LocalTimeZone(datetime.tzinfo):
    """Local timezone class that defers to the time module."""

    # TODO: Inline _mktime() and _localtime().

    def _mktime(self, dt):
        assert dt.tzinfo is self
        return time.mktime((dt.year, dt.month, dt.day,
                            dt.hour, dt.minute, dt.second,
                            -1, -1, -1))

    def _localtime(self, dt):
        return time.localtime(self._mktime(dt))

    def _isdst(self, dt):
        return time.daylight and self._localtime(dt).tm_isdst > 0

    def _zoff(self, dt):
        return time.altzone if self._isdst(dt) else time.timezone

    def tzname(self, dt):
        if dt is None:
            return None
        dst = self._isdst(dt)
        return time.tzname[dst]

    def utcoffset(self, dt):
        if dt is None:
            return None
        zoff = self._zoff(dt)
        return datetime.timedelta(seconds=zoff)

    def dst(self, dt):
        if dt is None:
            return None
        zoff = self._zoff(dt)
        return datetime.timedelta(seconds=(time.timezone - zoff))

    # Inherit fromutc() from the base class.


class BetterLocalTimeZone(LocalTimeZone):

    def tzname(self, dt):
        if dt is None:
            return None
        tt = self._localtime(dt)
        return tt.tm_zone

    def _zoff(self, dt):
        tt = self._localtime(dt)
        return tt.tm_gmtoff


if not time.daylight:
    local_tz = datetime.timezone(time.timezone, time.tzname[0])
elif hasattr(time.localtime(), 'tm_zone') and hasattr(time.localtime(), 'tm_gmtoff'):
    local_tz = BetterLocalTimeZone()
else:
    local_tz = LocalTimeZone()

print(local_tz.__class__.__name__)
dt = datetime.datetime.now(tz=local_tz)
print(dt.strftime("%a %b %d %H:%M:%S %Y %Z (%z)"))
dt += datetime.timedelta(180)
print(dt.strftime("%a %b %d %H:%M:%S %Y %Z (%z)"))