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

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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
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41
Doc/library/time.rst
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@ -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