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      1 import sys
      2 import os
      3 import struct
      4 from array import array
      5 from collections import namedtuple
      6 from datetime import datetime, timedelta
      7 
      8 ttinfo = namedtuple('ttinfo', ['tt_gmtoff', 'tt_isdst', 'tt_abbrind'])
      9 
     10 class TZInfo:
     11     def __init__(self, transitions, type_indices, ttis, abbrs):
     12         self.transitions = transitions
     13         self.type_indices = type_indices
     14         self.ttis = ttis
     15         self.abbrs = abbrs
     16 
     17     @classmethod
     18     def fromfile(cls, fileobj):
     19         if fileobj.read(4).decode() != "TZif":
     20             raise ValueError("not a zoneinfo file")
     21         fileobj.seek(20)
     22         header = fileobj.read(24)
     23         tzh = (tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
     24                tzh_timecnt, tzh_typecnt, tzh_charcnt) = struct.unpack(">6l", header)
     25         transitions = array('i')
     26         transitions.fromfile(fileobj, tzh_timecnt)
     27         if sys.byteorder != 'big':
     28             transitions.byteswap()
     29 
     30         type_indices = array('B')
     31         type_indices.fromfile(fileobj, tzh_timecnt)
     32 
     33         ttis = []
     34         for i in range(tzh_typecnt):
     35             ttis.append(ttinfo._make(struct.unpack(">lbb", fileobj.read(6))))
     36 
     37         abbrs = fileobj.read(tzh_charcnt)
     38 
     39         self = cls(transitions, type_indices, ttis, abbrs)
     40         self.tzh = tzh
     41 
     42         return self
     43 
     44     def dump(self, stream, start=None, end=None):
     45         for j, (trans, i) in enumerate(zip(self.transitions, self.type_indices)):
     46             utc = datetime.utcfromtimestamp(trans)
     47             tti = self.ttis[i]
     48             lmt = datetime.utcfromtimestamp(trans + tti.tt_gmtoff)
     49             abbrind = tti.tt_abbrind
     50             abbr = self.abbrs[abbrind:self.abbrs.find(0, abbrind)].decode()
     51             if j > 0:
     52                 prev_tti = self.ttis[self.type_indices[j - 1]]
     53                 shift = " %+g" % ((tti.tt_gmtoff - prev_tti.tt_gmtoff) / 3600)
     54             else:
     55                 shift = ''
     56             print("%s UTC = %s %-5s isdst=%d" % (utc, lmt, abbr, tti[1]) + shift, file=stream)
     57 
     58     @classmethod
     59     def zonelist(cls, zonedir='/usr/share/zoneinfo'):
     60         zones = []
     61         for root, _, files in os.walk(zonedir):
     62             for f in files:
     63                 p = os.path.join(root, f)
     64                 with open(p, 'rb') as o:
     65                     magic =  o.read(4)
     66                 if magic == b'TZif':
     67                     zones.append(p[len(zonedir) + 1:])
     68         return zones
     69 
     70 if __name__ == '__main__':
     71     if len(sys.argv) < 2:
     72         zones = TZInfo.zonelist()
     73         for z in zones:
     74             print(z)
     75         sys.exit()
     76     filepath = sys.argv[1]
     77     if not filepath.startswith('/'):
     78         filepath = os.path.join('/usr/share/zoneinfo', filepath)
     79     with open(filepath, 'rb') as fileobj:
     80         tzi = TZInfo.fromfile(fileobj)
     81     tzi.dump(sys.stdout)
     82