[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Paul Ganssle  added the comment:

Bug reported to BSD here: 
https://marc.info/?l=openbsd-bugs=153728102618747=2

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[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Paul Ganssle  added the comment:

I do think this is an active bug in OpenBSD's ISO calculations, here: 
https://github.com/openbsd/src/blob/b66614995ab119f75167daaa7755b34001836821/lib/libc/time/wcsftime.c#L326

I re-created this algorithm in Python and at the beginning of the year it gives 
the wrong answer at the beginning of the year in about 50% of years. I have 
spent some time trying to understand the way the algorithm is *supposed* to 
work, but I don't totally understand what it's doing. I'll report this to 
OpenBSD.

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[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Paul Ganssle  added the comment:

@Serhiy Looking more closely at #13414, I think there's a good chance that 
we've just discovered a different bug in OpenBSD's implementation of wcsftime 
(or strftime). Looks like OpenBSD 6.1 was released in 2017, which should have 
been years after the fix from #13414 was released.

It seems that OpenBSD does not have a bug tracker per se, and I can't see if 
this bug has been reported. I can try to install OpenBSD in a VM later and try 
to reproduce it, but if it's a bug in OpenBSD, I see some possible options:

1. Add an exception to the test suite on OpenBSD (to be removed or pinned when 
it's fixed in OpenBSD)

2. If the bug is just in wcsftime and not in strftime, it may be fixed by 
switching to using strftime as is done on Windows: 
https://github.com/python/cpython/blob/master/Modules/timemodule.c#L673

I have never tested it, but it's possible this will impact performance, and if 
it's a bad enough hit it may not be worth sacrificing general performance to 
avoid a bug in a corner case.

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[issue31635] test_strptime failure on OpenBSD

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I used OpenBSD 6.1. I'll check on more modern versions when have chance.

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[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Paul Ganssle  added the comment:

This appears to be a duplicate of issue #13414, which was resolved as fixed in 
BSD. @serhiy Are you using a very old version of BSD?

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[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Paul Ganssle  added the comment:

I think this is the relevant test: 
https://github.com/python/cpython/blob/3.7/Lib/test/test_strptime.py#L536

The issue seems to be in `strftime` rather than in `strptime`. According to 
Serhiy's paste, it seems that `datetime.datetime.strftime("%G %V %w")` on BSD 
results in "1904 53 0", whereas on Linux it results in "1904 52 0".

I suspect the confusion *may* be related to the fact that ISO weekdays go 
Monday (1) to Sunday (7), where as %w goes Sunday (0) to Saturday (6).

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[issue31635] test_strptime failure on OpenBSD

[Paul Ganssle]

Change by Paul Ganssle :


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nosy: +p-ganssle

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[issue31635] test_strptime failure on OpenBSD

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


--
nosy: +xtreak

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[issue31635] test_strptime failure on OpenBSD

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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nosy: +davin

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[issue31635] test_strptime failure on OpenBSD

[Serhiy Storchaka]

New submission from Serhiy Storchaka :

$ ./python -m test -vuall test_strptime
...
==
FAIL: test_week_of_year_and_day_of_week_calculation 
(test.test_strptime.CalculationTests) [Jan 1 on Sunday] (date=(1905, 1, 1), 
format='%G %V %w')
--
Traceback (most recent call last):
  File "/home/serhiy/py/cpython3.7/Lib/test/test_strptime.py", line 508, in 
test_helper
self.assertEqual(strp_output[:3], ymd_tuple, msg)
AssertionError: Tuples differ: (1905, 1, 8) != (1905, 1, 1)

First differing element 2:
8
1

- (1905, 1, 8)
?   ^

+ (1905, 1, 1)
?   ^
 : '1904 53 0': 374 != 1

==
...
FAILED (failures=16, skipped=1)

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components: Library (Lib)
messages: 303319
nosy: belopolsky, lemburg, serhiy.storchaka
priority: normal
severity: normal
status: open
title: test_strptime failure on OpenBSD
type: behavior

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