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import sys

import os

import struct

from array import array

from collections import namedtuple

from datetime import datetime

ttinfo = namedtuple('ttinfo', ['tt_gmtoff', 'tt_isdst', 'tt_abbrind'])

class TZInfo:

def __init__(self, transitions, type_indices, ttis, abbrs):

self.transitions = transitions

self.type_indices = type_indices

self.ttis = ttis

self.abbrs = abbrs

@classmethod

def fromfile(cls, fileobj):

if fileobj.read(4).decode() != "TZif":

raise ValueError("not a zoneinfo file")

fileobj.seek(20)

header = fileobj.read(24)

tzh = (tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,

tzh_timecnt, tzh_typecnt, tzh_charcnt) = struct.unpack(">6l", header)

transitions = array('i')

transitions.fromfile(fileobj, tzh_timecnt)

if sys.byteorder != 'big':

transitions.byteswap()

type_indices = array('B')

type_indices.fromfile(fileobj, tzh_timecnt)

ttis = []

for i in range(tzh_typecnt):

ttis.append(ttinfo._make(struct.unpack(">lbb", fileobj.read(6))))

abbrs = fileobj.read(tzh_charcnt)

self = cls(transitions, type_indices, ttis, abbrs)

self.tzh = tzh

return self

def dump(self, stream, start=None, end=None):

for j, (trans, i) in enumerate(zip(self.transitions, self.type_indices)):

utc = datetime.utcfromtimestamp(trans)

tti = self.ttis[i]

lmt = datetime.utcfromtimestamp(trans + tti.tt_gmtoff)

abbrind = tti.tt_abbrind

abbr = self.abbrs[abbrind:self.abbrs.find(0, abbrind)].decode()

if j > 0:

prev_tti = self.ttis[self.type_indices[j - 1]]

shift = " %+g" % ((tti.tt_gmtoff - prev_tti.tt_gmtoff) / 3600)

else:

shift = ''

print("%s UTC = %s %-5s isdst=%d" % (utc, lmt, abbr, tti[1]) + shift, file=stream)

@classmethod

def zonelist(cls, zonedir='/usr/share/zoneinfo'):

zones = []

for root, _, files in os.walk(zonedir):

for f in files:

p = os.path.join(root, f)

with open(p, 'rb') as o:

magic = o.read(4)

if magic == b'TZif':

zones.append(p[len(zonedir) + 1:])

return zones

if __name__ == '__main__':

if len(sys.argv) < 2:

zones = TZInfo.zonelist()

for z in zones:

print(z)

sys.exit()

filepath = sys.argv[1]

if not filepath.startswith('/'):

filepath = os.path.join('/usr/share/zoneinfo', filepath)

with open(filepath, 'rb') as fileobj:

tzi = TZInfo.fromfile(fileobj)

tzi.dump(sys.stdout)

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