tz.py

Python的一个ORM,现在很火

"""
Copyright (c) 2003-2005  Gustavo Niemeyer <[e-mail]>

This module offers extensions to the standard python 2.3+
datetime module.
"""
__author__ = "Gustavo Niemeyer <[e-mail]>"
__license__ = "PSF License"

import datetime
import struct
import time
import sys
import os

relativedelta = None
parser = None
rrule = None

__all__ = ["tzutc", "tzoffset", "tzlocal", "tzfile", "tzrange",
           "tzstr", "tzical", "tzwin", "tzwinlocal", "gettz"]

try:
    from dateutil.tzwin import tzwin, tzwinlocal
except (ImportError, OSError):
    tzwin, tzwinlocal = None, None

ZERO = datetime.timedelta(0)
EPOCHORDINAL = datetime.datetime.utcfromtimestamp(0).toordinal()

class tzutc(datetime.tzinfo):

    def utcoffset(self, dt):
        return ZERO
     
    def dst(self, dt):
        return ZERO

    def tzname(self, dt):
        return "UTC"

    def __eq__(self, other):
        return (isinstance(other, tzutc) or
                (isinstance(other, tzoffset) and other._offset == ZERO))

    def __ne__(self, other):
        return not self.__eq__(other)

    def __repr__(self):
        return "%s()" % self.__class__.__name__

    __reduce__ = object.__reduce__

class tzoffset(datetime.tzinfo):

    def __init__(self, name, offset):
        self._name = name
        self._offset = datetime.timedelta(seconds=offset)

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

    def dst(self, dt):
        return ZERO

    def tzname(self, dt):
        return self._name

    def __eq__(self, other):
        return (isinstance(other, tzoffset) and
                self._offset == other._offset)

    def __ne__(self, other):
        return not self.__eq__(other)

    def __repr__(self):
        return "%s(%s, %s)" % (self.__class__.__name__,
                               `self._name`,
                               self._offset.days*86400+self._offset.seconds)

    __reduce__ = object.__reduce__

class tzlocal(datetime.tzinfo):

    _std_offset = datetime.timedelta(seconds=-time.timezone)
    if time.daylight:
        _dst_offset = datetime.timedelta(seconds=-time.altzone)
    else:
        _dst_offset = _std_offset

    def utcoffset(self, dt):
        if self._isdst(dt):
            return self._dst_offset
        else:
            return self._std_offset

    def dst(self, dt):
        if self._isdst(dt):
            return self._dst_offset-self._std_offset
        else:
            return ZERO

    def tzname(self, dt):
        return time.tzname[self._isdst(dt)]

    def _isdst(self, dt):
        # We can't use mktime here. It is unstable when deciding if
        # the hour near to a change is DST or not.
        # 
        # timestamp = time.mktime((dt.year, dt.month, dt.day, dt.hour,
        #                         dt.minute, dt.second, dt.weekday(), 0, -1))
        # return time.localtime(timestamp).tm_isdst
        #
        # The code above yields the following result:
        #
        #>>> import tz, datetime
        #>>> t = tz.tzlocal()
        #>>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        #'BRDT'
        #>>> datetime.datetime(2003,2,16,0,tzinfo=t).tzname()
        #'BRST'
        #>>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        #'BRST'
        #>>> datetime.datetime(2003,2,15,22,tzinfo=t).tzname()
        #'BRDT'
        #>>> datetime.datetime(2003,2,15,23,tzinfo=t).tzname()
        #'BRDT'
        #
        # Here is a more stable implementation:
        #
        timestamp = ((dt.toordinal() - EPOCHORDINAL) * 86400
                     + dt.hour * 3600
                     + dt.minute * 60
                     + dt.second)
        return time.localtime(timestamp+time.timezone).tm_isdst

    def __eq__(self, other):
        if not isinstance(other, tzlocal):
            return False
        return (self._std_offset == other._std_offset and
                self._dst_offset == other._dst_offset)
        return True

    def __ne__(self, other):
        return not self.__eq__(other)

    def __repr__(self):
        return "%s()" % self.__class__.__name__

    __reduce__ = object.__reduce__

class _ttinfo(object):
    __slots__ = ["offset", "delta", "isdst", "abbr", "isstd", "isgmt"]

    def __init__(self):
        for attr in self.__slots__:
            setattr(self, attr, None)

    def __repr__(self):
        l = []
        for attr in self.__slots__:
            value = getattr(self, attr)
            if value is not None:
                l.append("%s=%s" % (attr, `value`))
        return "%s(%s)" % (self.__class__.__name__, ", ".join(l))

    def __eq__(self, other):
        if not isinstance(other, _ttinfo):
            return False
        return (self.offset == other.offset and
                self.delta == other.delta and
                self.isdst == other.isdst and
                self.abbr == other.abbr and
                self.isstd == other.isstd and
                self.isgmt == other.isgmt)

    def __ne__(self, other):
        return not self.__eq__(other)

    def __getstate__(self):
        state = {}
        for name in self.__slots__:
            state[name] = getattr(self, name, None)
        return state

    def __setstate__(self, state):
        for name in self.__slots__:
            if name in state:
                setattr(self, name, state[name])

class tzfile(datetime.tzinfo):

    # http://www.twinsun.com/tz/tz-link.htm
    # ftp://elsie.nci.nih.gov/pub/tz*.tar.gz
    
    def __init__(self, fileobj):
        if isinstance(fileobj, basestring):
            self._filename = fileobj
            fileobj = open(fileobj)
        elif hasattr(fileobj, "name"):
            self._filename = fileobj.name
        else:
            self._filename = `fileobj`

        # From tzfile(5):
        #
        # The time zone information files used by tzset(3)
        # begin with the magic characters "TZif" to identify
        # them as time zone information files, followed by
        # sixteen bytes reserved for future use, followed by
        # six four-byte values of type long, written in a
        # ``standard'' byte order (the high-order  byte
        # of the value is written first).

        if fileobj.read(4) != "TZif":
            raise ValueError, "magic not found"

        fileobj.read(16)

        (
         # The number of UTC/local indicators stored in the file.
         ttisgmtcnt,

         # The number of standard/wall indicators stored in the file.
         ttisstdcnt,
         
         # The number of leap seconds for which data is
         # stored in the file.
         leapcnt,

         # The number of "transition times" for which data
         # is stored in the file.
         timecnt,

         # The number of "local time types" for which data
         # is stored in the file (must not be zero).
         typecnt,

         # The  number  of  characters  of "time zone
         # abbreviation strings" stored in the file.
         charcnt,

        ) = struct.unpack(">6l", fileobj.read(24))

        # The above header is followed by tzh_timecnt four-byte
        # values  of  type long,  sorted  in ascending order.
        # These values are written in ``standard'' byte order.
        # Each is used as a transition time (as  returned  by
        # time(2)) at which the rules for computing local time
        # change.

        if timecnt:
            self._trans_list = struct.unpack(">%dl" % timecnt,
                                             fileobj.read(timecnt*4))
        else:
            self._trans_list = []

        # Next come tzh_timecnt one-byte values of type unsigned
        # char; each one tells which of the different types of
        # ``local time'' types described in the file is associated
        # with the same-indexed transition time. These values
        # serve as indices into an array of ttinfo structures that
        # appears next in the file.
        
        if timecnt:
            self._trans_idx = struct.unpack(">%dB" % timecnt,
                                            fileobj.read(timecnt))
        else:
            self._trans_idx = []
        
        # Each ttinfo structure is written as a four-byte value
        # for tt_gmtoff  of  type long,  in  a  standard  byte
        # order, followed  by a one-byte value for tt_isdst
        # and a one-byte  value  for  tt_abbrind.   In  each
        # structure, tt_gmtoff  gives  the  number  of
        # seconds to be added to UTC, tt_isdst tells whether
        # tm_isdst should be set by  localtime(3),  and
        # tt_abbrind serves  as an index into the array of
        # time zone abbreviation characters that follow the
        # ttinfo structure(s) in the file.

        ttinfo = []

        for i in range(typecnt):
            ttinfo.append(struct.unpack(">lbb", fileobj.read(6)))

        abbr = fileobj.read(charcnt)

        # Then there are tzh_leapcnt pairs of four-byte
        # values, written in  standard byte  order;  the
        # first  value  of  each pair gives the time (as
        # returned by time(2)) at which a leap second
        # occurs;  the  second  gives the  total  number of
        # leap seconds to be applied after the given time.
        # The pairs of values are sorted in ascending order
        # by time.

        # Not used, for now
        if leapcnt:
            leap = struct.unpack(">%dl" % leapcnt*2,
                                 fileobj.read(leapcnt*8))

        # Then there are tzh_ttisstdcnt standard/wall
        # indicators, each stored as a one-byte value;
        # they tell whether the transition times associated
        # with local time types were specified as standard
        # time or wall clock time, and are used when
        # a time zone file is used in handling POSIX-style
        # time zone environment variables.

        if ttisstdcnt:
            isstd = struct.unpack(">%db" % ttisstdcnt,
                                  fileobj.read(ttisstdcnt))