psycopg2/lib/tz.py

# psycopg/tz.py - tzinfo implementation
#
# Copyright (C) 2003-2004 Federico Di Gregorio  <fog@debian.org>
#
# 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, 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 MERCHANTIBILITY
# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.

import datetime
import time


ZERO = datetime.timedelta(0)

class FixedOffsetTimezone(datetime.tzinfo):
    """Fixed offset in minutes east from UTC.

    This is exactly the implementation found in Python 2.3.x documentation,
    with a small change to the __init__ method to allow for pickling and a
    default name in the form 'sHH:MM' ('s' is the sign.)
    """
    _name = None
    _offset = ZERO
    
    def __init__(self, offset=None, name=None):
        if offset is not None:
            self._offset = datetime.timedelta(minutes = offset)
        if name is not None:
            self._name = name

    def utcoffset(self, dt):
        return self._offset

    def tzname(self, dt):
        if self._name is not None:
            return self._name
        else:
            seconds = self._offset.seconds + self._offset.days * 86400
            hours, seconds = divmod(seconds, 3600)
            minutes = seconds/60
            if minutes:
                return "%+03d:%d" % (hours, minutes)
            else:
                return "%+03d" % hours
            
    def dst(self, dt):
        return ZERO


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

class LocalTimezone(datetime.tzinfo):
    """Platform idea of local timezone.

    This is the exact implementation from the Pyhton 2.3 documentation.
    """
    
    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()

# TODO: pre-generate some interesting time zones?