DEPR: weekofyear

[mroeschke]

Now that isocalendar is available on Timestamp, DatetimeIndex and the dt accessor, weekofyear already exists in isocalendar and can be deprecated.

[jorisvandenbossche]

Is such a deprecation needed?

Yes, it gives some duplication in functionality, but:

• Those existing attributes have been around for a long time, and people have been happily using them.
• Personally, I think weekofyear is more accessible (more logical to think of, easier findable with tab completion) than through isocalendar
• isocalendar is also doing more work (and thus slower) if all you need is the week number

[mgmarino]

I'm ok with not deprecating, but I have a few comments:

• Just because they're used a lot doesn't mean they're used correctly and I would argue that weekofyear could lead to a lot of hidden issues. That is, people don't realize that it's the ISO week and might not realize that year doesn't always match up with it. Indeed a quick search through the issues here yields a number of reported "bugs". By deprecating, it becomes harder to mess up: you would force people to actively choose the ISO calendar. Also, if they need a week with some other definition (starting on e.g. Sunday), then they can use the period functionality to do this.
• Regarding slowness, if this is an issue than maybe it could be addressed some other way (e.g. caching).

[jreback]

perf is a non issue here

the only issue is cost of deprecation va correctness

eg realize that u r using iso

+1 on actually having an informative api