Commit e0997604 authored by M. Huang's avatar M. Huang
Browse files

missing file

parent cc2ab08f
#!/usr/bin/env python
"""Get TAI-UTC difference in seconds for a given time using tzdata.
i.e., find the number of seconds that must be added to UTC to compute
TAI for any timestamp at or after the given time[1].
>>> from datetime import datetime
>>> import leapseconds
>>> leapseconds.dTAI_UTC_from_utc(datetime(2005, 1, 1, tzinfo = timezone.utc))
datetime.timedelta(0, 32)
>>> leapseconds.utc_to_tai(datetime(2015, 7, 1, tzinfo = timezone.utc))
datetime.datetime(2015, 7, 1, 0, 0, 36, tzinfo=datetime.timezone.utc)
>>> leapseconds.tai_to_utc(datetime(2015, 7, 1, 0, 0, 36, tzinfo = timezone.utc))
datetime.datetime(2015, 7, 1, 0, 0, tzinfo=datetime.timezone.utc)
>>> leapseconds.tai_to_utc(datetime(2015, 7, 1, 0, 0, 35, tzinfo = timezone.utc)) # leap second
datetime.datetime(2015, 7, 1, 0, 0, tzinfo=datetime.timezone.utc)
>>> leapseconds.tai_to_utc(datetime(2015, 7, 1, 0, 0, 34, tzinfo = timezone.utc))
datetime.datetime(2015, 6, 30, 23, 59, 59, tzinfo=datetime.timezone.utc)
Python 2.6+, Python 3, Jython, Pypy support.
[1]: https://github.com/eggert/tz/blob/master/leap-seconds.list
[2]: https://github.com/eggert/tz/blob/master/tzfile.h
[3]: https://github.com/eggert/tz/blob/master/zic.c
[4]: http://datacenter.iers.org/eop/-/somos/5Rgv/latest/16
"""
from __future__ import with_statement
from collections import namedtuple
from datetime import datetime, timedelta, timezone
from struct import Struct
from warnings import warn
from functools import partial
__all__ = ['leapseconds', 'LeapSecond',
'dTAI_UTC_from_utc', 'dTAI_UTC_from_tai',
'tai_to_utc', 'utc_to_tai',
'gps_to_utc', 'utc_to_gps',
'tai_to_gps', 'gps_to_tai']
__version__ = "0.1.0"
# from timezone/tzfile.h [2] (the file is in public domain)
"""
struct tzhead {
char tzh_magic[4]; /* TZ_MAGIC */
char tzh_version[1]; /* '\0' or '2' or '3' as of 2013 */
char tzh_reserved[15]; /* reserved--must be zero */
char tzh_ttisgmtcnt[4]; /* coded number of trans. time flags */
char tzh_ttisstdcnt[4]; /* coded number of trans. time flags */
char tzh_leapcnt[4]; /* coded number of leap seconds */
char tzh_timecnt[4]; /* coded number of transition times */
char tzh_typecnt[4]; /* coded number of local time types */
char tzh_charcnt[4]; /* coded number of abbr. chars */
};
# from zic.c[3] (the file is in public domain)
convert(const int_fast32_t val, char *const buf)
{
register int i;
register int shift;
unsigned char *const b = (unsigned char *) buf;
for (i = 0, shift = 24; i < 4; ++i, shift -= 8)
b[i] = val >> shift;
}
# val = 0x12345678
# (val >> 24) & 0xff, (val >> 16) & 0xff, (val >> 8) & 0xff, val & 0xff
# 0x12 0x34 0x56 0x78
# therefore "coded number" means big-endian 32-bit integer
"""
dTAI_GPS = timedelta(seconds=19) # constant offset
LeapSecond = namedtuple('LeapSecond', 'utc dTAI_UTC') # tai = utc + dTAI_UTC
sentinel = LeapSecond(utc=datetime.max.replace(
tzinfo=timezone.utc), dTAI_UTC=timedelta(0))
def leapseconds(tzfiles=['/usr/share/zoneinfo/right/UTC',
'/usr/lib/zoneinfo/right/UTC'],
use_fallback=True):
"""Extract leap seconds from *tzfiles*."""
for filename in tzfiles:
try:
file = open(filename, 'rb')
except IOError:
continue
else:
break
else: # no break
if not use_fallback:
raise ValueError('Unable to open any tzfile: %s' % (tzfiles,))
else:
return _fallback()
with file:
header = Struct('>4s c 15x 6i') # see struct tzhead above
(magic, version, _, _, leapcnt, timecnt, typecnt,
charcnt) = header.unpack_from(file.read(header.size))
if magic != "TZif".encode():
raise ValueError('Wrong magic %r in tzfile: %s' % (
magic, file.name))
if version not in '\x0023'.encode():
warn('Unsupported version %r in tzfile: %s' % (
version, file.name), RuntimeWarning)
if leapcnt == 0:
if not use_fallback:
raise ValueError("No leap seconds in tzfile: %s" % (
file.name))
else:
return _fallback()
"""# from tzfile.h[2] (the file is in public domain)
. . .header followed by. . .
tzh_timecnt (char [4])s coded transition times a la time(2)
tzh_timecnt (unsigned char)s types of local time starting at above
tzh_typecnt repetitions of
one (char [4]) coded UT offset in seconds
one (unsigned char) used to set tm_isdst
one (unsigned char) that's an abbreviation list index
tzh_charcnt (char)s '\0'-terminated zone abbreviations
tzh_leapcnt repetitions of
one (char [4]) coded leap second transition times
one (char [4]) total correction after above
"""
file.read(timecnt * 5 + typecnt * 6 + charcnt) # skip
result = [LeapSecond(datetime(1972, 1, 1), timedelta(seconds=10))]
nleap_seconds = 10
tai_epoch_as_tai = datetime(1970, 1, 1, 0, 0, 10)
buf = Struct(">2i")
for _ in range(leapcnt): # read leap seconds
t, cnt = buf.unpack_from(file.read(buf.size))
dTAI_UTC = nleap_seconds + cnt
utc = tai_epoch_as_tai + timedelta(seconds=t - dTAI_UTC + 1)
assert utc - datetime(utc.year, utc.month, utc.day) == timedelta(0)
result.append(LeapSecond(utc, timedelta(seconds=dTAI_UTC)))
result.append(sentinel)
return result
def _fallback():
"""Leap seconds list if no tzfiles are available."""
td = timedelta
dt_utc = partial(datetime, tzinfo=timezone.utc)
return [
# appropriate
LeapSecond(utc=dt_utc(1958, 1, 1, 0, 0), dTAI_UTC=td(0, 0)),
LeapSecond(utc=dt_utc(1961, 1, 1, 0, 0), dTAI_UTC=td(0, 1.442818)),
LeapSecond(utc=dt_utc(1961, 8, 1, 0, 0), dTAI_UTC=td(0, 1.372818)),
LeapSecond(utc=dt_utc(1962, 1, 1, 0, 0), dTAI_UTC=td(0, 1.845858)),
LeapSecond(utc=dt_utc(1963, 11, 1, 0, 0), dTAI_UTC=td(0, 1.945858)),
LeapSecond(utc=dt_utc(1964, 1, 1, 0, 0), dTAI_UTC=td(0, 3.240130)),
LeapSecond(utc=dt_utc(1964, 4, 1, 0, 0), dTAI_UTC=td(0, 3.340130)),
LeapSecond(utc=dt_utc(1964, 9, 1, 0, 0), dTAI_UTC=td(0, 3.440130)),
LeapSecond(utc=dt_utc(1965, 1, 1, 0, 0), dTAI_UTC=td(0, 3.540130)),
LeapSecond(utc=dt_utc(1965, 3, 1, 0, 0), dTAI_UTC=td(0, 3.640130)),
LeapSecond(utc=dt_utc(1965, 7, 1, 0, 0), dTAI_UTC=td(0, 3.740130)),
LeapSecond(utc=dt_utc(1965, 9, 1, 0, 0), dTAI_UTC=td(0, 3.840130)),
LeapSecond(utc=dt_utc(1966, 1, 1, 0, 0), dTAI_UTC=td(0, 4.313170)),
LeapSecond(utc=dt_utc(1968, 2, 1, 0, 0), dTAI_UTC=td(0, 4.213170)),
LeapSecond(utc=dt_utc(1972, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 10)),
LeapSecond(utc=dt_utc(1972, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 11)),
LeapSecond(utc=dt_utc(1973, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 12)),
LeapSecond(utc=dt_utc(1974, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 13)),
LeapSecond(utc=dt_utc(1975, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 14)),
LeapSecond(utc=dt_utc(1976, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 15)),
LeapSecond(utc=dt_utc(1977, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 16)),
LeapSecond(utc=dt_utc(1978, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 17)),
LeapSecond(utc=dt_utc(1979, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 18)),
LeapSecond(utc=dt_utc(1980, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 19)),
LeapSecond(utc=dt_utc(1981, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 20)),
LeapSecond(utc=dt_utc(1982, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 21)),
LeapSecond(utc=dt_utc(1983, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 22)),
LeapSecond(utc=dt_utc(1985, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 23)),
LeapSecond(utc=dt_utc(1988, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 24)),
LeapSecond(utc=dt_utc(1990, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 25)),
LeapSecond(utc=dt_utc(1991, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 26)),
LeapSecond(utc=dt_utc(1992, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 27)),
LeapSecond(utc=dt_utc(1993, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 28)),
LeapSecond(utc=dt_utc(1994, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 29)),
LeapSecond(utc=dt_utc(1996, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 30)),
LeapSecond(utc=dt_utc(1997, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 31)),
LeapSecond(utc=dt_utc(1999, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 32)),
LeapSecond(utc=dt_utc(2006, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 33)),
LeapSecond(utc=dt_utc(2009, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 34)),
LeapSecond(utc=dt_utc(2012, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 35)),
LeapSecond(utc=dt_utc(2015, 7, 1, 0, 0), dTAI_UTC=timedelta(0, 36)),
LeapSecond(utc=dt_utc(2017, 1, 1, 0, 0), dTAI_UTC=timedelta(0, 37)),
sentinel]
def dTAI_UTC_from_utc(utc_time):
"""TAI time = utc_time + dTAI_UTC_from_utc(utc_time)."""
return _dTAI_UTC(utc_time, lambda ls: ls.utc)
def dTAI_UTC_from_tai(tai_time):
"""UTC time = tai_time - dTAI_UTC_from_tai(tai_time)."""
return _dTAI_UTC(tai_time, lambda ls: ls.utc + ls.dTAI_UTC)
def _dTAI_UTC(time, leapsecond_to_time, leapseconds=leapseconds):
"""Get TAI-UTC difference in seconds for a given time.
>>> from datetime import datetime, timedelta
>>> _dTAI_UTC(datetime(1972, 1, 1, tzinfo = timezone.utc), lambda ls: ls.utc)
datetime.timedelta(0, 10)
>>> tai = lambda ls: ls.utc + ls.dTAI_UTC
>>> _dTAI_UTC(datetime(2015, 7, 1, 0, 0, 34, tzinfo = timezone.utc), tai)
datetime.timedelta(0, 35)
>>> _dTAI_UTC(datetime(2015, 7, 1, 0, 0, 35, tzinfo = timezone.utc), tai) # leap second
datetime.timedelta(0, 35)
>>> _dTAI_UTC(datetime(2015, 7, 1, 0, 0, 36, tzinfo = timezone.utc), tai)
datetime.timedelta(0, 36)
Bulletin C 51 says "NO leap second will be introduced at the end
of June 2016."[4] and therefore UTC-TAI is still 36
at 27 June 2016:
>>> _dTAI_UTC(datetime(2016, 6, 27, tzinfo = timezone.utc), lambda ls: ls.utc)
datetime.timedelta(0, 36)
"""
leapseconds_list = leapseconds()
transition_times = list(map(leapsecond_to_time, leapseconds_list))
if time < transition_times[0]:
raise ValueError("Dates before %s are not supported, got %r" % (
transition_times[0], time))
for i, (start, end) in enumerate(zip(transition_times,
transition_times[1:])):
if start <= time < end:
return leapseconds_list[i].dTAI_UTC
assert 0
def tai_to_utc(tai_time):
"""Convert TAI time given as datetime object to UTC time."""
return tai_time - dTAI_UTC_from_tai(tai_time)
def utc_to_tai(utc_time):
"""Convert UTC time given as datetime object to TAI time."""
return utc_time + dTAI_UTC_from_utc(utc_time)
def gps_to_utc(gps_time):
"""Convert GPS time given as datetime object to UTC time."""
return tai_to_utc(gps_to_tai(gps_time))
def utc_to_gps(utc_time):
"""Convert UTC time given as datetime object to GPS time."""
return tai_to_gps(utc_to_tai(utc_time))
def tai_to_gps(tai_time):
"""Convert TAI time given as datetime object to GPS time."""
return tai_time - dTAI_GPS
def gps_to_tai(gps_time):
"""Convert GPS time given as datetime object to TAI time."""
return gps_time + dTAI_GPS
if __name__ == "__main__":
import doctest
doctest.testmod()
import json
assert all(ls.dTAI_UTC == timedelta(seconds=ls.dTAI_UTC.seconds,
microseconds=ls.dTAI_UTC.microseconds)
for ls in leapseconds()) # ~+200 leap second until 2100
print(json.dumps([dict(utc=t.utc, tai=t.utc + t.dTAI_UTC,
dTAI_UTC=t.dTAI_UTC.seconds)
for t in leapseconds()],
default=str, indent=4, sort_keys=True))
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