[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Jason R. Coombs]

Jason R. Coombs  added the comment:

The tempora library implements a [portable 
strftime](https://tempora.readthedocs.io/en/latest/index.html#tempora.strftime).

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Chris Larson]

Chris Larson  added the comment:

Has there been any work/progress on this? Alternatively, what suggested work 
around/mitigations are suggested?

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Fredrik Bengtsson]

Fredrik Bengtsson  added the comment:

This also causes an issue when using stftime and strptime together on Linux 
(Ubuntu 20.04.1 LTS).
When encoding a datetime using strftime and decoding with strptime using the 
same pattern an error is raised if year < 1000.

Example:
>>> pattern = "%Y-%m-%d"
>>> datetime.strptime(
... datetime(1, 1, 1).strftime(pattern),
... pattern
... )
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib/python3.8/_strptime.py", line 568, in _strptime_datetime
tt, fraction, gmtoff_fraction = _strptime(data_string, format)
  File "/usr/lib/python3.8/_strptime.py", line 349, in _strptime
raise ValueError("time data %r does not match format %r" %
ValueError: time data '1-01-01' does not match format '%Y-%m-%d'

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[STINNER Victor]

STINNER Victor  added the comment:

> I'd like for Python to provide a portable implementation of strftime instead 
> of just documenting that the version isn't portable.

If someone wants to do that, I suggest to first start with a project on PyPI. 
It sounds like a tricky project. Date, time, locales and localization are hard 
problems!

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Jason R. Coombs]

Jason R. Coombs  added the comment:

In issue39103, I filed a bug relating to this issue.

I'd like for Python to provide a portable implementation of strftime instead of 
just documenting that the version isn't portable.

Given that this ticket assigned to 'docs' suggests that a portable version is 
out of the question. Can we expand the scope of this issue to actually 
providing a portable version?

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Paul Ganssle]

Change by Paul Ganssle :


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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Paul Ganssle]

Change by Paul Ganssle :


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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Ned Deily]

Ned Deily  added the comment:

(See also msg307413 in duplicate Issue32195 for more discussion.)

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Roundup Robot]

Roundup Robot added the comment:

New changeset e54224e8d6a9 by Victor Stinner in branch 'default':
Revert change 291d47954618
https://hg.python.org/cpython/rev/e54224e8d6a9

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[STINNER Victor]

STINNER Victor added the comment:

Elena's issue13305.diff:

"Zero padding can be forced on some platforms by using e.g. ``%4Y``"

Sorry, I still doesn't understand the change. %4Y doesn't work with strptime() 
and it only work with strftime() on very few platforms.

Can you explain when %4Y should be used? strftime() and/or strptime()? Which 
platform?

To me, it looks wrong to document %4Y since it almost never works...

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[STINNER Victor]

STINNER Victor added the comment:

>> About Elena Oat's patch issue13305.diff: I'm not sure that
>> strftime("%4Y") works on all platforms

> It doesn't, that's what the patch is trying to document.

Oh. I confirm: %4Y gives "4Y" for any year on FreeBSD and Mac OS X, it raises 
ValueError("Invalid format string") on Windows, etc.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Ezio Melotti]

Ezio Melotti added the comment:

> About Elena Oat's patch issue13305.diff: I'm not sure that
> strftime("%4Y") works on all platforms

It doesn't, that's what the patch is trying to document.
AFAICT it works on my Linux (but not on yours), it gives '4Y' on Mac, and 
raises an error on Windows.  This should depend on the libc used by system, so 
the same OS can give different results depending on which libc it uses, and the 
only sure thing is that %4Y is not a portable solution.
FWIW the patch LGTM (except a couple minor nits -- zero-pad should be 
hyphenated and there should be a double space after the dot), but I'm not sure 
if it's better mentioning platforms at all or just being vague and say that it 
works on some platforms but not others and leave up to the user figuring out 
where.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[STINNER Victor]

STINNER Victor added the comment:

acucci's patch doc.patch suggests to use format "%4Y". Problem: I tried it on 
Linux, and it looks like it doesn't work.

>>> datetime.datetime.strptime("1980", "%Y")
datetime.datetime(1980, 1, 1, 0, 0)
>>> datetime.datetime.strptime("1980", "%4Y")
Traceback (most recent call last):
  ...
ValueError: '4' is a bad directive in format '%4Y'

Or maybe I misunderstood the doc change. Do you suggest to use %4Y format with 
strptime(), with strftime() or with both?

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Roundup Robot]

Roundup Robot added the comment:

New changeset 291d47954618 by Victor Stinner in branch 'default':
Always test datetime.strftime("%4Y")
https://hg.python.org/cpython/rev/291d47954618

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[STINNER Victor]

STINNER Victor added the comment:

About Elena Oat's patch issue13305.diff: I'm not sure that strftime("%4Y") 
works on all platforms, so I enabled the test on strftime("%4Y"). I will check 
our buildbots.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Elena Oat]

Elena Oat added the comment:

I submitted a patch for documentation changes related to strftime "%Y" 
directive inconsistencies. I am not sure that specifying the OS is correct, 
because I haven't tested the inconsistencies on all Linux PCs, Windows versions 
or OS X. I still left them there though, so let me know what's your opinion on 
it.

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Added file: http://bugs.python.org/file42136/issue13305.diff

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Alessandro Cucci]

Changes by Alessandro Cucci :


Added file: http://bugs.python.org/file41476/doc.patch

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Martin Panter]

Martin Panter added the comment:

At the bottom of  
it suggests that this four-digit field width specifier is not portable. Does 
that also hold for the datetime version? It seems like a bad idea to recommend 
an unportable workaround for a portability problem.

Also, in the patch it is not clear if you are referring to strptime(), 
strftime(), or both. On Linux, datetime.strptime(..., "%4Y") fails for me.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Ezio Melotti]

Ezio Melotti added the comment:

> Also, using %4Y seems to consistently produce zero-padded values across
> different platforms.

Actually I was wrong.  Based on some more testing I did on Linux and Windows 8 
and the previous comments in this thread, it seems that, with 1 as year:
* '%4Y' does produces '0001' on Linux but gives a value error on Windows and 
'4Y' on OS X;
* '%Y' produces '1' on Linux and '0001' on Windows and OS X;

So the problem is only on Linux and only with years <1000, where to have a 
zero-padded value %4Y can be used instead.
I don't know if these results are true for all versions of Linux/Win/OSX, so 
the note could just say that:
1) some platforms (e.g. Linux) don't zero-pad years <1000;
2) some platforms (e.g. Linux) support %4Y to add padding, but this doesn't 
work on other platforms.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Ezio Melotti]

Ezio Melotti added the comment:

See msg146972 -- AFAIU the padding of %Y is inconsistent for years <1000 (e.g. 
0042 vs 42), and this is not documented in the note (2) of 
https://docs.python.org/3/library/datetime.html#strftime-and-strptime-behavior
Also, using %4Y seems to consistently produce zero-padded values across 
different platforms.

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[issue13305] datetime.strftime("%Y") not consistent for years < 1000

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

Can someone recap the status of this issue?  It is classified as a 
documentation bug, but I don't see a clear statement of what is wrong with the 
documentation.

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[STINNER Victor]

STINNER Victor victor.stin...@haypocalc.com added the comment:

Did your commit fix the issue or not?

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

Florent Xicluna florent.xicl...@gmail.com added the comment:

I understand that the issue is because the C standard does not specify the 
length of the string returned by '%Y'.

The changeset 230f0956aaa3 adds a test to verify that either '%Y' or '%4Y' 
returns a 4-digits value usable to produce ISO-8601 representations.

Now it is a documentation issue: add a comment to the %Y specifier saying 
that the padding is not applicable to all platforms and in such case the %4Y 
specifier should return the 4-digit value.

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assignee:  - docs@python
components: +Documentation
dependencies:  -external strftime for Python?
nosy: +docs@python
superseder:  - external strftime for Python?

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[STINNER Victor]

STINNER Victor victor.stin...@haypocalc.com added the comment:

Since the changeset 55a3b563f0dbed04af317f632f7f3c0f6abe175b, test_strptime is 
failing on AMD64 Gentoo Wide 3.x buildbot:

==
FAIL: test_strptime (test.test_time.TimeTestCase)
--
Traceback (most recent call last):
  File 
/home/buildbot/buildarea/3.x.ochtman-gentoo-amd64/build/Lib/test/test_time.py,
 line 159, in test_strptime
time.strptime(strf_output, format)
ValueError: time data 'LMT' does not match format '%Z'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File 
/home/buildbot/buildarea/3.x.ochtman-gentoo-amd64/build/Lib/test/test_time.py,
 line 162, in test_strptime
(format, strf_output))
AssertionError: conversion specifier '%Z' failed with 'LMT' input.

--

http://www.python.org/dev/buildbot/all/builders/AMD64%20Gentoo%20Wide%203.x/builds/2661

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

Florent Xicluna florent.xicl...@gmail.com added the comment:

other test_time related errors are followed with issue 13309, issue 13312 and 
issue 13313

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[STINNER Victor]

STINNER Victor victor.stin...@haypocalc.com added the comment:

Le 01/11/2011 00:07, Roundup Robot a écrit :

 Roundup Robotdevn...@psf.upfronthosting.co.za  added the comment:

 New changeset 3f025427f02b by Florent Xicluna in branch 'default':
 Fix regression due to changeset 2096158376e5 (issue #13305).
 http://hg.python.org/cpython/rev/3f025427f02b

I don't like this hack. If there is a bug in time.strftime(), we need to 
fix time.strftime(), not xmlrpclib.

Is there a test for the hack?

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Roundup Robot]

Roundup Robot devn...@psf.upfronthosting.co.za added the comment:

New changeset 230f0956aaa3 by Florent Xicluna in branch 'default':
Strengthen the tests for format '%Y', in relation with issue #13305.
http://hg.python.org/cpython/rev/230f0956aaa3

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

New submission from Florent Xicluna florent.xicl...@gmail.com:

See msg146725 on issue 13291.

on linux
 datetime(1,  2, 10, 11, 41, 23).strftime(%Y)
'1'

on osx
 datetime(1,  2, 10, 11, 41, 23).strftime(%Y)
'0001'


 datetime.strptime('0001', '%Y')
datetime.datetime(1, 1, 1, 0, 0)

 datetime.strptime('1', '%Y')
ValueError: time data '1' does not match format '%Y'

--
components: Library (Lib)
messages: 146740
nosy: flox
priority: normal
severity: normal
stage: test needed
status: open
title: datetime.strftime(%Y) not consistent for years  1000
type: behavior
versions: Python 2.7, Python 3.2, Python 3.3

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

Florent Xicluna florent.xicl...@gmail.com added the comment:

FWIW, issue #1777412 added support for years  1000 to Python 3.3 strftime.

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stage: test needed - needs patch
versions:  -Python 2.7, Python 3.2

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Ezio Melotti]

Changes by Ezio Melotti ezio.melo...@gmail.com:


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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Alexander Belopolsky]

Alexander Belopolsky alexander.belopol...@gmail.com added the comment:

I am not sure this can be fixed without distributing our own implementation of 
strftime.  See issue 3173.

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

Florent Xicluna florent.xicl...@gmail.com added the comment:

There's many discrepancies between OS X and Linux about time formatting...

OS X
 from datetime import datetime
 datetime(1900, 1, 1).strftime(%6Y)
'6Y'

Linux
 from datetime import datetime
 datetime(1900, 1, 1).strftime(%6Y)
'001900'

BTW, these discrepancies are already mentioned:
http://docs.python.org/dev/library/datetime.html#strftime-strptime-behavior

“The full set of format codes supported varies across platforms, because Python 
calls the platform C library’s strftime() function, and platform variations are 
common.”

We should had an asterisk to the %Y saying that the padding is not consistent 
across platforms.

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Florent Xicluna]

Florent Xicluna florent.xicl...@gmail.com added the comment:

Proposed patch to fix the issue in xmlrpc.client

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Added file: http://bugs.python.org/file23577/issue13305_xmlrpc_patch.diff

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[issue13305] datetime.strftime(%Y) not consistent for years 1000

[Roundup Robot]

Roundup Robot devn...@psf.upfronthosting.co.za added the comment:

New changeset 3f025427f02b by Florent Xicluna in branch 'default':
Fix regression due to changeset 2096158376e5 (issue #13305).
http://hg.python.org/cpython/rev/3f025427f02b

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