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datetime.strptime at the turn of the year #67323

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torm mannequin opened this issue Dec 30, 2014 · 4 comments
Closed

datetime.strptime at the turn of the year #67323

torm mannequin opened this issue Dec 30, 2014 · 4 comments
Labels
type-bug An unexpected behavior, bug, or error

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@torm
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torm mannequin commented Dec 30, 2014

BPO 23134
Nosy @abalkin, @vadmium, @serhiy-storchaka
Superseder
  • bpo-23136: BUG in how _strptime() handles week 0
    		•
    Files
  • strptimetest.c
    		•

    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 = None
closed_at = <Date 2014-12-31.16:30:33.370>
created_at = <Date 2014-12-30.18:04:02.231>
labels = ['type-bug']
title = 'datetime.strptime at the turn of the year'
updated_at = <Date 2014-12-31.16:30:33.367>
user = 'https://bugs.python.org/torm'

    bugs.python.org fields:

    activity = <Date 2014-12-31.16:30:33.367>
actor = 'belopolsky'
assignee = 'none'
closed = True
closed_date = <Date 2014-12-31.16:30:33.370>
closer = 'belopolsky'
components = []
creation = <Date 2014-12-30.18:04:02.231>
creator = 'torm'
dependencies = []
files = ['37566']
hgrepos = []
issue_num = 23134
keywords = []
message_count = 4.0
messages = ['233213', '233215', '233239', '233249']
nosy_count = 4.0
nosy_names = ['belopolsky', 'martin.panter', 'serhiy.storchaka', 'torm']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '23136'
type = 'behavior'
url = 'https://bugs.python.org/issue23134'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4', 'Python 3.5']
    @torm
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    torm mannequin commented Dec 30, 2014

    I've found wrong behaviour datetime.strptim function at the turn of the year.

    I've created datetime object base on the week number (%W), year (%Y) and day of week (%w). The date for Tuesday in the first week in 2015 is wrong:

    >>> from datetime import datetime
>>> datetime.strptime('%s %s %s' % (0, 2015, 1), '%W %Y %w').date()
datetime.date(2014, 12, 29) # OK

>>> datetime.strptime('%s %s %s' % (0, 2015, 2), '%W %Y %w').date()
datetime.date(2015, 1, 1) # WRONG !!!

>>> datetime.strptime('%s %s %s' % (0, 2015, 3), '%W %Y %w').date()
datetime.date(2014, 12, 31) # OK

>>> datetime.strptime('%s %s %s' % (0, 2015, 4), '%W %Y %w').date()
datetime.date(2015, 1, 1) # OK

>>> datetime.strptime('%s %s %s' % (0, 2015, 5), '%W %Y %w').date()
datetime.date(2015, 1, 2) # OK

>>> datetime.strptime('%s %s %s' % (0, 2015, 6), '%W %Y %w').date()
datetime.date(2015, 1, 3) # OK

>>> datetime.strptime('%s %s %s' % (0, 2015, 0), '%W %Y %w').date()
datetime.date(2015, 1, 4) # OK

    The same error exists in another years.

    Link to my post about this on stackoverflow:
    http://stackoverflow.com/questions/27708833/why-does-datetime-strptime-get-an-incorrect-date-for-tuesday-in-the-week-0-of

    @torm torm mannequin added the type-bug An unexpected behavior, bug, or error label Dec 30, 2014
    @serhiy-storchaka
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    In C the strptime function doesn't return valid data if an input is invalid.

    $ ./strptimetest "0 2015 1" "%W %Y %w"
2015-00--2 00:00:00
$ ./strptimetest "0 2015 2" "%W %Y %w"
2015-00--1 00:00:00
$ ./strptimetest "0 2015 3" "%W %Y %w"
2015-00-00 00:00:00
$ ./strptimetest "0 2015 4" "%W %Y %w"
2015-01-01 00:00:00
$ ./strptimetest "0 2015 5" "%W %Y %w"
2015-01-02 00:00:00
$ ./strptimetest "0 2015 6" "%W %Y %w"
2015-01-03 00:00:00
$ ./strptimetest "0 2015 7" "%W %Y %w"
2015-01-00 00:00:00

    So this behavior likely is not a bug and doesn't need to be fixed in maintained releases. But it would be good to make strptime() more consistant and either extend it to support week and weekday numbers out of current valid range, or raise an exception.

    @vadmium
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    vadmium commented Dec 31, 2014

    bpo-23136 looks like a duplicate, but has a potential patch

    @abalkin
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    abalkin commented Dec 31, 2014

    Closing as a duplicate of bpo-23136.

    @abalkin abalkin closed this as completed Dec 31, 2014
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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