[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

Committed in r81566 (trunk), r81568 (py3k), r81569 (release26-maint), r81570 
(release31-maint).

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stage: commit review -> committed/rejected
status: open -> closed

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[issue7150] datetime operations spanning MINYEAR give bad results

[Mark Dickinson]

Mark Dickinson  added the comment:

As an aside, I dislike the fact that the datetime module uses a C 'int' for 
date ordinals, and clearly assumes that it'll be at least 32 bits.  int could 
be as small as 16 bits on some systems (small embedded systems?).  But that's 
another issue.

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[issue7150] datetime operations spanning MINYEAR give bad results

[Mark Dickinson]

Mark Dickinson  added the comment:

The patch looks good to me.  Please apply!

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assignee: mark.dickinson -> belopolsky
resolution:  -> accepted

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[issue7150] datetime operations spanning MINYEAR give bad results

[Mark Dickinson]

Mark Dickinson  added the comment:

I'll take a look at this patch later today.

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assignee: belopolsky -> mark.dickinson

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[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

I've untabified my last patch and added a NEWS entry.  I believe it is ready 
for commit review.  Mark?

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nosy: +mark.dickinson
stage: patch review -> commit review
Added file: http://bugs.python.org/file17466/issue7150a.diff

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[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Changes by Alexander Belopolsky :


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assignee:  -> belopolsky
nosy: +belopolsky -Alexander.Belopolsky

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[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

My patch includes unit tests and I tested it on Mac OS X.  Anand, what kind of 
testing do you have in mind?

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versions: +Python 2.7, Python 3.2, Python 3.3

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[issue7150] datetime operations spanning MINYEAR give bad results

[Anand B Pillai]

Anand B Pillai  added the comment:

Can someone update this issue ? Is the 2nd patch tested... ?

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[issue7150] datetime operations spanning MINYEAR give bad results

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc  added the comment:

No, because normally distributions do not use debug builds.
but that's the reason why tests are needed: they must pass with asserts enabled.

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[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

Aha!  My reliance on asserts() was misguided.  With the debug build:

>>> t0-d2
Assertion failed: (ordinal >= 1), function ord_to_ymd, file 
/Users/sasha/Work/python-svn/trunk/Modules/datetimemodule.c, line 269.
Abort trap

Should we reclassify this bug as a crash?

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[issue7150] datetime operations spanning MINYEAR give bad results

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

Given

assert(*m > 0);
assert(*d > 0);

at the end of normalize_y_m_d(), it looks like at lest 1 <=*month and 1 <=*day 
are redundant.

A closer look also reveals 

assert(1 <= *m && *m <= 12);

in the middle of normalize_y_m_d().  This seems to leave only *day <=31 
possibly relevant.

I suspect that out of bounds day surviving normalize_y_m_d() is a logical error 
in that function that needs to be fixed and an assert() added at the end.  The 
proposed patch appears to cure the symptom rather than the actual flaw.

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nosy: +Alexander.Belopolsky

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[issue7150] datetime operations spanning MINYEAR give bad results

[Anand B Pillai]

Anand B Pillai  added the comment:

The problem seems to be in the "normalize_date" function in
datetimemodule.c. It is checking for a valid year range, but not
checking for a valid month or day range. 

I have a patch which fixes this problem. It checks for month range
(1<=m<=12) and day range(1<=d<=31). Here is Python with the patch.

an...@anand-laptop:~/projects/python/py3k$ ./python
Python 3.2a0 (py3k:75627, Oct 25 2009, 14:28:21) 
[GCC 4.3.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
Traceback (most recent call last):
  File "/home/anand/.pythonrc", line 2, in 
import readline
ImportError: No module named readline
>>> import datetime
>>> t0=datetime.datetime(1,1,1)
>>> d1,d2,d3=map(datetime.timedelta, range(1,4))
>>> t0-d1
Traceback (most recent call last):
  File "", line 1, in 
OverflowError: date value out of range
>>> t0-d2
Traceback (most recent call last):
  File "", line 1, in 
OverflowError: date value out of range
>>> t0-d3
Traceback (most recent call last):
  File "", line 1, in 
OverflowError: date value out of range
>>> d0=datetime.timedelta(0)
>>> t0-d0
datetime.datetime(1, 1, 1, 0, 0)
>>> 

Svn diff is attached.

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Added file: http://bugs.python.org/file15194/datetimemodule.c.svndiff

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[issue7150] datetime operations spanning MINYEAR give bad results

[Anand B Pillai]

Anand B Pillai  added the comment:

The issue is present in Python 3.0 and 2.5 as well.

Python 2.5.1 (r251:54863, Jul 17 2008, 13:21:31)
[GCC 4.3.1 20080708 (Red Hat 4.3.1-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
>>> t0=datetime.datetime(1,1,1)
>>> d1,d2,d3=map(datetime.timedelta, range(1,4))
>>> t0-d1
Traceback (most recent call last):
  File "", line 1, in 
OverflowError: date value out of range
>>> t0-d2
datetime.datetime(1, 0, 255, 0, 0)

I think this is bug in datetime for all Python versions

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[issue7150] datetime operations spanning MINYEAR give bad results

[mark.leander]

New submission from mark.leander :

The datetime module documentation would imply that operations that cause
dates to fall outside the MINYEAR--MAXYEAR range should raise
OverflowError. The interpreter session below shows that this is not
always the case, and that such operations may cause bogus and
inconsistent results.

Python 2.6.3 (r263rc1:75186, Oct  2 2009, 20:40:30) [MSC v.1500 32 bit
(Intel)]
on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
>>> t0=datetime.datetime(1,1,1)
>>> d1, d2, d3 = map(datetime.timedelta, range(1,4))
# The following is expected and accoring to the docs:
>>> t0-d1
Traceback (most recent call last):
  File "", line 1, in 
OverflowError: date value out of range

# The following is completely bogus:
>>> t0-d2
datetime.datetime(1, 0, 255, 0, 0)

# The two following behaving differently may be very confusing,
# the second one is correct
>>> t0-d2+d3
datetime.datetime(1, 8, 15, 0, 0)
>>> t0+d3-d2
datetime.datetime(1, 1, 2, 0, 0)
>>>

--
components: Library (Lib)
messages: 94132
nosy: mark.leander
severity: normal
status: open
title: datetime operations spanning MINYEAR give bad results
type: behavior
versions: Python 2.6

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