[issue35841] Datetime strftime() does not return correct week numbers for 2019
New submission from Tommy Rowland : This relates to the calculation of the week number from a given datetime, when calling the strftime method. If you call isocalendar() on the datetime.datetime object for the date ‘2018-12-31’, the week number returned is 1, which is correct. This is the same when checking the week attribute for the pandas timestamp equivalent. However, when you call strftime on this object (either datetime or timestamp), passing the ‘%W’ offset string, it returns 53, and then returns 00 for the remainder of the week. It seems that the rest of the weeks in 2019 are out by 1 when returned using this function. This issue seems to be present with the strptime function also. -- components: Extension Modules, Windows files: Python Datetime Issue.JPG messages: 334462 nosy: paul.moore, steve.dower, tim.golden, tr12, zach.ware priority: normal severity: normal status: open title: Datetime strftime() does not return correct week numbers for 2019 type: behavior versions: Python 2.7, Python 3.6 Added file: https://bugs.python.org/file48083/Python Datetime Issue.JPG ___ Python tracker <https://bugs.python.org/issue35841> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue35841] Datetime strftime() does not return correct week numbers for 2019
Tommy Rowland added the comment:
Hi Paul,
Thank you for the clarification. I can see that %V does indeed return the
correct week number. It seems that when calling strftime, it is possible to
use this in conjunction with %y, but when calling strptime, it is not. Is
this also intended behaviour?
Best regards,
Tommy
On Mon, Jan 28, 2019 at 4:44 PM Paul Ganssle wrote:
>
> Paul Ganssle added the comment:
>
> I think this is not a bug. bpo-35535 is probably also intended behavior,
> but that is less certain.
>
> The misunderstanding here is that %W does not give you the ISO week
> number, from the documentation:
>
> %W: Week number of the year (Monday as the first day of the week) as a
> decimal number.
> All days in a new year preceding the first Monday are considered
> to be in week 0.
>
>
> If you want the ISO week number, I think you need %V, which *is* the ISO
> week:
>
> >>> datetime(2018, 12, 31).strftime("%V %W")
>
> '01 53'
>
> I believe this ticket can be closed.
>
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