Docs for WeekArchiveView are misleading about %W

[Michal Petrucha]

The ​docs state:

The '%W' format uses the ISO week format and its week begins on a Monday. The '%W' format is the same in both the strftime() and the date.

However, as established in #7380, this is not true (another example is the week starting on 2015-11-16, which is week 47 according to date, but 46 according to strftime()). This section of the docs should be rephrased into a warning that '%W' and 'W' are not compatible with each other.

[Tim Graham]

Would be great if you could submit a patch since you apparently understand the issue.

[Michal Petrucha]

I'll try to submit a PR later this week, unless somebody beats me to it.

[Michal Petrucha]

As promised, ​https://github.com/django/django/pull/6171.

[Tim Graham]

Left some comments for improvement, please uncheck "Patch needs improvement" when updating.

[Michal Petrucha]

Thanks for the feedback; I'm trying to incorporate it into the patch.

One interesting thing I found is that the GNU libc supports an additional format string, '%V', which uses the same ISO 8601 numbering as the 'W' format character of the date template filter. (​http://linux.die.net/man/3/strftime) However, it is not documented in the Python docs for strftime, since the Python docs are limited to the C89 standard. On the other hand, '%V' was introduced in C99, which hopefully means that any reasonably recent system supports this format string.

Anyway, I think it might be worth adding support for '%V' in WeekArchiveView. That way we get a combination of out-of-the-box date formatters and parsers that work in templates and Python code alike. A potential pitfall is that requires a different year in certain corner cases with first and last weeks in a given year, which is '%G' for strftime and 'o' for date. This means a bit of special-casing would be required in WeekArchiveView, and clear docs pointing out the difference, but I still think it's worth it.

Is it okay to implement this in the current PR, or should I open a new one?

[Tim Graham <timograham@…>]

In 468c6a3b:

[1.9.x] Fixed #26217 -- Added a warning about format strings to WeekArchiveView docs.

Backport of fe8ea3ba3ba709b3d6c39da046f0883a296e6441 from master

[Tim Graham <timograham@…>]

In fe8ea3ba:

Fixed #26217 -- Added a warning about format strings to WeekArchiveView docs.

[Michal Petrucha]

For the sake of completeness, in case someone stumbles upon this ticket, using '%V' as the format string to parse the week number is a dead end, because while strftime is a function specified in the C standard, strptime is not, which means CPython needs to include its own implementation of strptime, and that only implements the set of strftime format strings mandated by C89.

[Tim Graham <timograham@…>]

In 2109975:

Refs #26217 -- Fixed typo in docs/ref/class-based-views/generic-date-based.txt.

[Tim Graham <timograham@…>]

In d38da1cc:

[1.9.x] Refs #26217 -- Fixed typo in docs/ref/class-based-views/generic-date-based.txt.

Backport of 2109975e901440da70e29d0f330a600bc2d37e9a from master