in functions/predictionLambda/dateutil/tz/tz.py [0:0]
def _read_tzfile(self, fileobj):
out = _tzfile()
# 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).decode() != "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:
out.trans_list_utc = list(struct.unpack(">%dl" % timecnt,
fileobj.read(timecnt*4)))
else:
out.trans_list_utc = []
# 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:
out.trans_idx = struct.unpack(">%dB" % timecnt,
fileobj.read(timecnt))
else:
out.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).decode()
# 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 (but seek for correct file position)
if leapcnt:
fileobj.seek(leapcnt * 8, os.SEEK_CUR)
# 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))
# Finally, there are tzh_ttisgmtcnt UTC/local
# indicators, each stored as a one-byte value;
# they tell whether the transition times associated
# with local time types were specified as UTC or
# local time, and are used when a time zone file
# is used in handling POSIX-style time zone envi-
# ronment variables.
if ttisgmtcnt:
isgmt = struct.unpack(">%db" % ttisgmtcnt,
fileobj.read(ttisgmtcnt))
# Build ttinfo list
out.ttinfo_list = []
for i in range(typecnt):
gmtoff, isdst, abbrind = ttinfo[i]
gmtoff = _get_supported_offset(gmtoff)
tti = _ttinfo()
tti.offset = gmtoff
tti.dstoffset = datetime.timedelta(0)
tti.delta = datetime.timedelta(seconds=gmtoff)
tti.isdst = isdst
tti.abbr = abbr[abbrind:abbr.find('\x00', abbrind)]
tti.isstd = (ttisstdcnt > i and isstd[i] != 0)
tti.isgmt = (ttisgmtcnt > i and isgmt[i] != 0)
out.ttinfo_list.append(tti)
# Replace ttinfo indexes for ttinfo objects.
out.trans_idx = [out.ttinfo_list[idx] for idx in out.trans_idx]
# Set standard, dst, and before ttinfos. before will be
# used when a given time is before any transitions,
# and will be set to the first non-dst ttinfo, or to
# the first dst, if all of them are dst.
out.ttinfo_std = None
out.ttinfo_dst = None
out.ttinfo_before = None
if out.ttinfo_list:
if not out.trans_list_utc:
out.ttinfo_std = out.ttinfo_first = out.ttinfo_list[0]
else:
for i in range(timecnt-1, -1, -1):
tti = out.trans_idx[i]
if not out.ttinfo_std and not tti.isdst:
out.ttinfo_std = tti
elif not out.ttinfo_dst and tti.isdst:
out.ttinfo_dst = tti
if out.ttinfo_std and out.ttinfo_dst:
break
else:
if out.ttinfo_dst and not out.ttinfo_std:
out.ttinfo_std = out.ttinfo_dst
for tti in out.ttinfo_list:
if not tti.isdst:
out.ttinfo_before = tti
break
else:
out.ttinfo_before = out.ttinfo_list[0]
# Now fix transition times to become relative to wall time.
#
# I'm not sure about this. In my tests, the tz source file
# is setup to wall time, and in the binary file isstd and
# isgmt are off, so it should be in wall time. OTOH, it's
# always in gmt time. Let me know if you have comments
# about this.
lastdst = None
lastoffset = None
lastdstoffset = None
lastbaseoffset = None
out.trans_list = []
for i, tti in enumerate(out.trans_idx):
offset = tti.offset
dstoffset = 0
if lastdst is not None:
if tti.isdst:
if not lastdst:
dstoffset = offset - lastoffset
if not dstoffset and lastdstoffset:
dstoffset = lastdstoffset
tti.dstoffset = datetime.timedelta(seconds=dstoffset)
lastdstoffset = dstoffset
# If a time zone changes its base offset during a DST transition,
# then you need to adjust by the previous base offset to get the
# transition time in local time. Otherwise you use the current
# base offset. Ideally, I would have some mathematical proof of
# why this is true, but I haven't really thought about it enough.
baseoffset = offset - dstoffset
adjustment = baseoffset
if (lastbaseoffset is not None and baseoffset != lastbaseoffset
and tti.isdst != lastdst):
# The base DST has changed
adjustment = lastbaseoffset
lastdst = tti.isdst
lastoffset = offset
lastbaseoffset = baseoffset
out.trans_list.append(out.trans_list_utc[i] + adjustment)
out.trans_idx = tuple(out.trans_idx)
out.trans_list = tuple(out.trans_list)
out.trans_list_utc = tuple(out.trans_list_utc)
return out