Comment by ethbr1
3 months ago
Or the story about the BillG review and Excel date math.
https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...
Which, incidentally, is a great primer for younger developers on both what obsessive software quality looks like and why datetimes are a hard problem.
I remember how date math is special there. A simple question: 30-01-2024 plus one month - what is the result date?
Well I had to try this in Excel and (after fighting the input format), it gave me
Fun. There is so much ambiguity in what “one month” means.
Polars has an offset-by function which is a bit more explicit about how you want to handle date math. “Calendar date” vs number of days.
Edit: just ran polars and I’m not in love with its answer either.
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