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strptime() can produce invalid date with negative year day #67906

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serhiy-storchaka opened this issue Mar 20, 2015 · 10 comments
Closed

strptime() can produce invalid date with negative year day #67906

serhiy-storchaka opened this issue Mar 20, 2015 · 10 comments
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@serhiy-storchaka
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stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@serhiy-storchaka
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BPO 23718
Nosy @malemburg, @abalkin, @serhiy-storchaka
Files
  • julian_date.patch
  • julian_date_v1.patch
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-03-12.08:55:19.765>
created_at = <Date 2015-03-20.11:30:32.291>
labels = ['type-bug', 'library']
title = 'strptime() can produce invalid date with negative year day'
updated_at = <Date 2016-03-12.08:55:19.764>
user = 'https://github.com/serhiy-storchaka'

    bugs.python.org fields:

    activity = <Date 2016-03-12.08:55:19.764>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-03-12.08:55:19.765>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-03-20.11:30:32.291>
creator = 'serhiy.storchaka'
dependencies = []
files = ['41877', '41936']
hgrepos = []
issue_num = 23718
keywords = ['patch']
message_count = 10.0
messages = ['238648', '259752', '259956', '260168', '260351', '260353', '260360', '261238', '261642', '261643']
nosy_count = 6.0
nosy_names = ['lemburg', 'belopolsky', 'python-dev', 'serhiy.storchaka', 'beng94', 'iaslan']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23718'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']
    @serhiy-storchaka
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    strptime() can produce invalid time with negative year day when parse year-week-weekday set. Such time is rejected by strftime(), so strptime/strftime roundtrip doesn't work.

    >>> t = time.strptime('2015 0 0', '%Y %U %w')
>>> t
time.struct_time(tm_year=2014, tm_mon=12, tm_mday=28, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=6, tm_yday=-3, tm_isdst=-1)
>>> time.strftime('%Y %U %w', t)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: day of year out of range

    @serhiy-storchaka serhiy-storchaka added stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Mar 20, 2015
    @beng94
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    beng94 mannequin commented Feb 6, 2016

    It looks interesting, let me try to solve this. At first it seems odd that _calc_julian_from_U_or_W returns -2, I guess something is wrong around there.

    @beng94
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    beng94 mannequin commented Feb 9, 2016

    I made a patch, that solves this issue.

    The problem was that there wasn't any Sunday (%w = 0) on the 0th week in 2015. 2015 started on Thursday, therefore the first Sunday was on 2014.12.28.

    julian variable is used to set the tm_yday, which was a minus value, as the given date was not in the same year.

    @serhiy-storchaka
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    Could you please add tests?

    @beng94
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    beng94 mannequin commented Feb 16, 2016

    Actually there are already test cases, but they test for the wrong behaviour. The very same example is tested there, but the test gives the expected result, so tm_yday = -3. My implementation returns 362, which looks more reasonable. So currently with my patch the test fails.

    See the tests here: https://github.com/python/cpython/blob/master/Lib/test/test_strptime.py#L523

    @serhiy-storchaka
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    Could you provide a patch? See also my comment on Rietveld (the "review" link).

    @beng94
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    beng94 mannequin commented Feb 16, 2016

    I've added a new patch, it uses an other way to calculate the number of days in a given year. I updated the tests, so now it doesn't fail, I also added some extra test cases to test leap years.

    @serhiy-storchaka serhiy-storchaka self-assigned this Mar 6, 2016
    @serhiy-storchaka
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    LGTM. Alexander, what would you say?

    @python-dev
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    python-dev mannequin commented Mar 12, 2016

    New changeset f03da87a79fa by Serhiy Storchaka in branch '3.5':
    Issue bpo-23718: Fixed parsing time in week 0 before Jan 1. Original patch by
    https://hg.python.org/cpython/rev/f03da87a79fa

    New changeset 4fb167ec3108 by Serhiy Storchaka in branch '2.7':
    Issue bpo-23718: Fixed parsing time in week 0 before Jan 1. Original patch by
    https://hg.python.org/cpython/rev/4fb167ec3108

    New changeset a7093386efaf by Serhiy Storchaka in branch 'default':
    Issue bpo-23718: Fixed parsing time in week 0 before Jan 1. Original patch by
    https://hg.python.org/cpython/rev/a7093386efaf

    @serhiy-storchaka
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    Thank you Tamás for your contribution.

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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