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Issue #10827: Changed the rules for 2-digit years. The time.asctime 

function will now format any year when time.accept2dyear is false and
will accept years >= 1000 otherwise.  The year range accepted by
time.mktime and time.strftime is still system dependent, but
time.mktime will now accept full range supported by the OS. Conversion
of 2-digit years to 4-digit is deprecated.
This commit is contained in:
Alexander Belopolsky 2011-01-07 19:59:19 +00:00
parent 696efdd03f
commit c64708ae48
4 changed files with 102 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
Doc/library/time.rst
View File

@ -24,9 +24,9 @@ An explanation of some terminology and conventions is in order.
.. index:: single: Year 2038
* The functions in this module do not handle dates and times before the epoch or
* The functions in this module may not handle dates and times before the epoch or
far in the future. The cut-off point in the future is determined by the C
library; for Unix, it is typically in 2038.
library; for 32-bit systems, it is typically in 2038.
.. index::
single: Year 2000
@ -34,20 +34,31 @@ An explanation of some terminology and conventions is in order.
.. _time-y2kissues:
* **Year 2000 (Y2K) issues**: Python depends on the platform's C library, which
* **Year 2000 (Y2K) issues**: Python depends on the platform's C library, which
generally doesn't have year 2000 issues, since all dates and times are
represented internally as seconds since the epoch. Functions accepting a
:class:`struct_time` (see below) generally require a 4-digit year. For backward
compatibility, 2-digit years are supported if the module variable
``accept2dyear`` is a non-zero integer; this variable is initialized to ``1``
unless the environment variable :envvar:`PYTHONY2K` is set to a non-empty
string, in which case it is initialized to ``0``. Thus, you can set
:envvar:`PYTHONY2K` to a non-empty string in the environment to require 4-digit
years for all year input. When 2-digit years are accepted, they are converted
according to the POSIX or X/Open standard: values 69-99 are mapped to 1969-1999,
and values 0--68 are mapped to 2000--2068. Values 100--1899 are always illegal.
Note that this is new as of Python 1.5.2(a2); earlier versions, up to Python
1.5.1 and 1.5.2a1, would add 1900 to year values below 1900.
represented internally as seconds since the epoch. Function :func:`strptime`
can parse 2-digit years when given ``%y`` format code. When 2-digit years are
parsed, they are converted according to the POSIX and ISO C standards: values
69--99 are mapped to 1969--1999, and values 0--68 are mapped to 2000--2068.
For backward compatibility, years with less than 4 digits are treated
specially by :func:`asctime`, :func:`mktime`, and :func:`strftime` functions
that operate on a 9-tuple or :class:`struct_time` values. If year (the first
value in the 9-tuple) is specified with less than 4 digits, its interpretation
depends on the value of ``accept2dyear`` variable.
If ``accept2dyear`` is true (default), a backward compatibility behavior is
invoked as follows:
- for 2-digit year, century is guessed according to POSIX rules for
``%y`` strptime format. A deprecation warning is issued when century
information is guessed in this way.
- for 3-digit or negative year, a :exc:`ValueError` exception is raised.
If ``accept2dyear`` is false (set by the program or as a result of a
non-empty value assigned to ``PYTHONY2K`` environment variable) all year
values are interpreted as given.
.. index::
single: UTC

62
Lib/test/test_time.py
View File

@ -3,6 +3,7 @@ import time
import unittest
import locale
import sysconfig
import warnings
class TimeTestCase(unittest.TestCase):
@ -19,10 +20,10 @@ class TimeTestCase(unittest.TestCase):
time.clock()
def test_conversions(self):
self.assertTrue(time.ctime(self.t)
== time.asctime(time.localtime(self.t)))
self.assertTrue(int(time.mktime(time.localtime(self.t)))
== int(self.t))
self.assertEqual(time.ctime(self.t),
time.asctime(time.localtime(self.t)))
self.assertEqual(int(time.mktime(time.localtime(self.t))),
int(self.t))
def test_sleep(self):
time.sleep(1.2)
@ -44,7 +45,7 @@ class TimeTestCase(unittest.TestCase):
# Check year [1900, max(int)]
self.assertRaises(ValueError, func,
(1899, 1, 1, 0, 0, 0, 0, 1, -1))
(999, 1, 1, 0, 0, 0, 0, 1, -1))
if time.accept2dyear:
self.assertRaises(ValueError, func,
(-1, 1, 1, 0, 0, 0, 0, 1, -1))
@ -97,7 +98,8 @@ class TimeTestCase(unittest.TestCase):
# No test for daylight savings since strftime() does not change output
# based on its value.
expected = "2000 01 01 00 00 00 1 001"
result = time.strftime("%Y %m %d %H %M %S %w %j", (0,)*9)
with support.check_warnings():
result = time.strftime("%Y %m %d %H %M %S %w %j", (0,)*9)
self.assertEqual(expected, result)
def test_strptime(self):
@ -141,14 +143,15 @@ class TimeTestCase(unittest.TestCase):
self.assertEqual(time.ctime(t), 'Sun Sep 16 01:03:52 1973')
t = time.mktime((2000, 1, 1, 0, 0, 0, 0, 0, -1))
self.assertEqual(time.ctime(t), 'Sat Jan 1 00:00:00 2000')
try:
bigval = time.mktime((10000, 1, 10) + (0,)*6)
except (ValueError, OverflowError):
# If mktime fails, ctime will fail too. This may happen
# on some platforms.
pass
else:
self.assertEqual(time.ctime(bigval)[-5:], '10000')
for year in [-100, 100, 1000, 2000, 10000]:
try:
testval = time.mktime((year, 1, 10) + (0,)*6)
except (ValueError, OverflowError):
# If mktime fails, ctime will fail too. This may happen
# on some platforms.
pass
else:
self.assertEqual(time.ctime(testval)[20:], str(year))
@unittest.skipIf(not hasattr(time, "tzset"),
"time module has no attribute tzset")
@ -239,14 +242,14 @@ class TimeTestCase(unittest.TestCase):
gt1 = time.gmtime(None)
t0 = time.mktime(gt0)
t1 = time.mktime(gt1)
self.assertTrue(0 <= (t1-t0) < 0.2)
self.assertAlmostEqual(t1, t0, delta=0.2)
def test_localtime_without_arg(self):
lt0 = time.localtime()
lt1 = time.localtime(None)
t0 = time.mktime(lt0)
t1 = time.mktime(lt1)
self.assertTrue(0 <= (t1-t0) < 0.2)
self.assertAlmostEqual(t1, t0, delta=0.2)
class TestLocale(unittest.TestCase):
def setUp(self):
@ -274,16 +277,18 @@ class TestAccept2Year(unittest.TestCase):
time.accept2dyear = self.saved_accept2dyear
def yearstr(self, y):
return time.strftime('%Y', (y,) + (0,) * 8)
# return time.strftime('%Y', (y,) + (0,) * 8)
return time.asctime((y,) + (0,) * 8).split()[-1]
def test_2dyear(self):
self.assertEqual(self.yearstr(0), '2000')
self.assertEqual(self.yearstr(69), '1969')
self.assertEqual(self.yearstr(68), '2068')
self.assertEqual(self.yearstr(99), '1999')
with support.check_warnings():
self.assertEqual(self.yearstr(0), '2000')
self.assertEqual(self.yearstr(69), '1969')
self.assertEqual(self.yearstr(68), '2068')
self.assertEqual(self.yearstr(99), '1999')
def test_invalid(self):
self.assertRaises(ValueError, self.yearstr, 1899)
self.assertRaises(ValueError, self.yearstr, 999)
self.assertRaises(ValueError, self.yearstr, 100)
self.assertRaises(ValueError, self.yearstr, -1)
@ -293,10 +298,15 @@ class TestAccept2YearBool(TestAccept2Year):
class TestDontAccept2Year(TestAccept2Year):
accept2dyear = 0
def test_2dyear(self):
self.assertRaises(ValueError, self.yearstr, 0)
self.assertRaises(ValueError, self.yearstr, 69)
self.assertRaises(ValueError, self.yearstr, 68)
self.assertRaises(ValueError, self.yearstr, 99)
self.assertEqual(self.yearstr(0), '0')
self.assertEqual(self.yearstr(69), '69')
self.assertEqual(self.yearstr(68), '68')
self.assertEqual(self.yearstr(99), '99')
self.assertEqual(self.yearstr(999), '999')
self.assertEqual(self.yearstr(9999), '9999')
def test_invalid(self):
pass
class TestDontAccept2YearBool(TestDontAccept2Year):
accept2dyear = False

8
Misc/NEWS
View File

@ -36,6 +36,14 @@ Core and Builtins
Library
-------
- Issue #10827: Changed the rules for 2-digit years. The time.asctime
function will now format any year when ``time.accept2dyear`` is
false and will accept years >= 1000 otherwise. The year range
accepted by ``time.mktime`` and ``time.strftime`` is still system
dependent, but ``time.mktime`` will now accept full range supported
by the OS. Conversion of 2-digit years to 4-digit is deprecated.
- Issue #7858: Raise an error properly when os.utime() fails under Windows
on an existing file.

47
Modules/timemodule.c
View File

@ -312,34 +312,42 @@ gettmarg(PyObject *args, struct tm *p)
&p->tm_wday, &p->tm_yday, &p->tm_isdst))
return 0;
/* XXX: Why 1900? If the goal is to interpret 2-digit years as those in
* 20th / 21st century according to the POSIX standard, we can just treat
* 0 <= y < 100 as special. Year 100 is probably too ambiguous and should
* be rejected, but years 101 through 1899 can be passed through.
/* If year is specified with less than 4 digits, its interpretation
* depends on the accept2dyear value.
*
* If accept2dyear is true (default), a backward compatibility behavior is
* invoked as follows:
*
* - for 2-digit year, century is guessed according to POSIX rules for
* %y strptime format: 21st century for y < 69, 20th century
* otherwise. A deprecation warning is issued when century
* information is guessed in this way.
*
* - for 3-digit or negative year, a ValueError exception is raised.
*
* If accept2dyear is false (set by the program or as a result of a
* non-empty value assigned to PYTHONY2K environment variable) all year
* values are interpreted as given.
*/
if (y < 1900) {
if (y < 1000) {
PyObject *accept = PyDict_GetItemString(moddict,
"accept2dyear");
int acceptval = accept != NULL && PyObject_IsTrue(accept);
if (acceptval == -1)
return 0;
if (acceptval) {
if (69 <= y && y <= 99)
y += 1900;
else if (0 <= y && y <= 68)
if (0 <= y && y < 69)
y += 2000;
else if (69 <= y && y < 100)
y += 1900;
else {
PyErr_SetString(PyExc_ValueError,
"year out of range");
return 0;
}
}
/* XXX: When accept2dyear is false, we don't have to reject y < 1900.
* Consider removing the following else-clause. */
else {
PyErr_SetString(PyExc_ValueError,
"year out of range");
return 0;
if (PyErr_WarnEx(PyExc_DeprecationWarning,
"Century info guessed for a 2-digit year.", 1) != 0)
return 0;
}
}
p->tm_year = y - 1900;
@ -462,6 +470,15 @@ time_strftime(PyObject *self, PyObject *args)
else if (!gettmarg(tup, &buf) || !checktm(&buf))
return NULL;
/* XXX: Reportedly, some systems have issues formating dates prior to year
* 1900. These systems should be identified and this check should be
* moved to appropriate system specific section below. */
if (buf.tm_year < 0) {
PyErr_Format(PyExc_ValueError, "year=%d is before 1900; "
"the strftime() method requires year >= 1900",
buf.tm_year + 1900);
}
/* Normalize tm_isdst just in case someone foolishly implements %Z
based on the assumption that tm_isdst falls within the range of
[-1, 1] */