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The other day at work I stumbled upon this bug and thought it was worth to write a blog post about. Spoiler: It has nothing to do with timezones!

TLDR: According to ISO standard 8601 (which is what Python's date.isocalendar().week uses for example), the first week of the year is the week with the first Thursday of the year. So sometimes the first few days of January belong to the last week of previous year, and sometimes the last few days of December belong to the first week of next year :D

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[-] ttayh@lemmy.zip 15 points 10 hours ago

The 1st day of the feek is not universal. I grew up with the week starting on sunday

[-] bleistift2@sopuli.xyz 12 points 9 hours ago

Yes, another thing in the neverending list of shit you have to learn at some point if you’re any kind of programmer.

Some people start their week on the wrong day.

[-] TehPers@beehaw.org 2 points 9 hours ago

Like ISO 8601. /s

[-] sergiu@lemmy.world 6 points 9 hours ago

Is this a thing outside the USA? It always bugs me when apps default to this. How does it make any sense for the week to start with the weekend?

[-] brisk@aussie.zone 4 points 6 hours ago
[-] sergiu@lemmy.world 1 points 24 minutes ago

A string is reversible, a week is not. A week has a beginning and an end.

[-] technohacker@programming.dev 2 points 7 hours ago

I've generally seen Sunday to be the start of the week here, my current headcanon for it is that Sunday and Saturday sort of book-end on both sides of the week, hence week-end_s_ plural

[-] sergiu@lemmy.world 1 points 17 minutes ago* (last edited 16 minutes ago)

I'm just curious how this works in practice.

When you say something like "Let's meet up this weekend", is it implied that you will meet on Saturday, since Sunday is the other end of next week, so technically a different weekend?

this post was submitted on 24 Mar 2026
72 points (100.0% liked)

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