#11197: django.utils.dateformat for 'W' is not correct
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Reporter: j...@gmx.de | Owner: nobody
Status: closed | Milestone:
Component: Template system | Version: 1.0
Resolution: invalid | Keywords: dateformat
Stage: Unreviewed | Has_patch: 0
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Changes (by kmtracey):
* status: new => closed
* needs_better_patch: => 0
* resolution: => invalid
* needs_tests: => 0
* needs_docs: => 0
Comment:
Summary says django.utils.dateformat for "W" is not correct, but near as I
can tell the results for dateformat "%W" are correct as documented here:
http://docs.djangoproject.com/en/dev/ref/templates/builtins/#now
which says %W returns the ISO-8601 week number of the year, with weeks
starting on Monday. Doing a little research, you'll find ISO-8601 week
number ranges from 1 to 53, where 1 is the the week with the first
Thursday in it. As Jan 1, 2009 was a Thursday, it was in week 1 by
ISO-8601 definition.
As you show, Django is returning 22 for this value for the date May 25,
2009, which agrees with the calendar on this page:
http://en.wikipedia.org/wiki/ISO_week_date. By ISO-8601 definitions May
25, 2009 is the first day of week 22.
The description goes into more detail about trouble resulting from using
the results of this dateformat option as input to the `week` parameter of
a generic view. The generic view uses Python's "%U" strftime formatting
definition for week number, found here:
http://docs.python.org/library/time.html#time.strftime. It is: "Week
number of the year (Sunday as the first day of the week) as a decimal
number [00,53]. All days in a new year preceding the first Sunday are
considered to be in week 0." By Python's definition Jan 1, 2009 was in
week 0, not week 1 as it is by ISO-8601 definition, and that leads to the
difference you observe for the May 25, 2009.
If there is some place within Django that tries to interchange these
values then there might be a bug there, but what you mention is a link you
have placed in your template that uses the result of %W dateformat
documented to return an ISO-8601-defined value as input to the
archive_week generic view `week` parameter that is documented
(http://docs.djangoproject.com/en/dev/ref/generic-views/#django-views-
generic-date-based-archive-week) to be "The week of the year for which the
archive serves (a string). Weeks start with Sunday." They are different
ways of numbering weeks and cannot be interchanged like that.
It's unfortunate that there are so many differing standards for numbering
and dates, and it would certainly be preferable if only one existed, but
that's not reality. Django supports retrieving an ISO-8601 week number in
one place but requires a different week numbering scheme elsewhere...not
ideal perhaps but all working as documented so I don't see a Django bug
here.
--
Ticket URL: <http://code.djangoproject.com/ticket/11197#comment:1>
Django <http://code.djangoproject.com/>
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