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# Source code for pywws.TimeZone

    #!/usr/bin/env python

    # pywws - Python software for USB Wireless Weather Stations
    # http://github.com/jim-easterbrook/pywws
    # Copyright (C) 2008-13  Jim Easterbrook  jim@jim-easterbrook.me.uk

    # This program is free software; you can redistribute it and/or
    # modify it under the terms of the GNU General Public License
    # as published by the Free Software Foundation; either version 2
    # of the License, or (at your option) any later version.

    # This program is distributed in the hope that it will be useful,
    # but WITHOUT ANY WARRANTY; without even the implied warranty of
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    # GNU General Public License for more details.

    # You should have received a copy of the GNU General Public License
    # along with this program; if not, write to the Free Software
    # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

    """Provide a couple of :py:class:`datetime.tzinfo` objects
    representing local time and UTC.

    Introduction
    ------------

    This module provides two :py:class:`datetime.tzinfo` objects
    representing UTC and local time zones. These are used to convert
    timestamps to and from UTC and local time. The weather station
    software stores data with UTC timestamps, to avoid problems with
    daylight savings time, but the template and plot programs output data
    with local times.

    The module is copied directly from the :py:class:`datetime.tzinfo`
    module documentation.

    Detailed API
    ------------

    """

    from datetime import tzinfo, timedelta, datetime
    import time as _time

    ZERO = timedelta(0)
    HOUR = timedelta(hours=1)

    class UTC(tzinfo):
        """UTC"""
        def utcoffset(self, dt):
            return ZERO
        def tzname(self, dt):
            return "UTC"
        def dst(self, dt):
            return ZERO
    utc = UTC()

    STDOFFSET = timedelta(seconds = -_time.timezone)
    if _time.daylight:
        DSTOFFSET = timedelta(seconds = -_time.altzone)
    else:
        DSTOFFSET = STDOFFSET
    DSTDIFF = DSTOFFSET - STDOFFSET

    class LocalTimezone(tzinfo):
        """Local time"""
        def utcoffset(self, dt):
            if self._isdst(dt):
                return DSTOFFSET
            else:
                return STDOFFSET
        def dst(self, dt):
            if self._isdst(dt):
                return DSTDIFF
            else:
                return ZERO
        def tzname(self, dt):
            return _time.tzname[self._isdst(dt)]
        def _isdst(self, dt):
            tt = (dt.year, dt.month, dt.day,
                  dt.hour, dt.minute, dt.second,
                  dt.weekday(), 0, -1)
            stamp = _time.mktime(tt)
            tt = _time.localtime(stamp)
            return tt.tm_isdst > 0
    Local = LocalTimezone()

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