IsoWeek

A numbered week of a year, as ISO 8601 counts them: 2026-W43.

Use it for weekly reports and rotas. A week's number doesn't always belong to the year of its days, so for a span of dates, use DateRange.

Shape

Its parts keep these rules, and a value that breaks one fails with the rule's name:

• week_in_year: week is 53 only in a year with 53 ISO weeks

Example

IsoWeek { year: 2026 week: 43 }

text.parse(raw, as: IsoWeek) reads one from text that comes from outside. Text that isn't one at all fails malformed, such as 2027-W53, 2026-W54 or 2026-W00.

Good to know

• Week 53 exists only in some years, so 2027-W53 is refused and 2026-W53 is not.
• == tells you whether two are the same, and < and list.sort_by compare and sort them.

In JSON

A string, in a request, a response or json.write:

"2026-W01""2026-W53"

Details