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1import sys
2import os
3import struct
4from array import array
5from collections import namedtuple
6from datetime import datetime
7
8ttinfo = namedtuple('ttinfo', ['tt_gmtoff', 'tt_isdst', 'tt_abbrind'])
9
10class 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
70if __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