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Comment by clord | Hacker News Reader

I suppose the Georgian calendar includes this gap officially? Or did the catholic world just jump from system to system? If it includes the gap officially, then yea, error is the right thing. But if we just moved to a new calendar, then arguably there should be no error. both calendars work for all dates continuously, and we could have conversion functions etc. The gap is just a big flag day (week.)

imo, if i am using Georgian i want that system even retroactively, just like projecting a date back into the stone age. I don't care that a particular geography or culture changed calendars.

So I suppose what is really going on is that some libraries are using Georgian consistently, and others are using some hybrid "civic" calendar that tracks what the romans and the catholics were using, so dates in history books make sense.

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Contracts and other similar types of financial instruments existed by this time there must be some way they handled it because something that said that it happened on a date that never occurred - sounds like what lawyers live for.

I’ll draft a Dubia so that when future popes change the calendar they will include a representative code sample and details about how we handle this.

(It’s important to remember that the pope and friends were operating much more like an international standards body than a religious leader when doing things like this.)

If a contract dated to the 4th October 1582 specifies you have 15 days to make payment, you would indeed need to know where that contract was signed to determine on what day that deadline expired.

And if there is a contract dated to the 6th October 1582, that does raise questions about its legitimacy (though in general misdating a contract does not void it, it would merely be one point of evidence in your argument that it's a forgery, just like using a particular font in a modern printed contract)

I was thinking of contracts that say "payment is due on 6 October" from before they knew the date of the change.

It's one of those "well technically" things programmers love to obsess over and the judge just says "everyone knows what was meant, stop being an idiot."

I assume there is a way to handle this in modern contract law. Surely people have forgotten how long the various months are and written contracts referring to April 31.

It's one of the reasons that they spell it out, or do things like "define what month is, and then the payment is due X months out" and not on a specific date.

> there must be some way they handled it because something that said that it happened on a date that never occurred - sounds like what lawyers live for.

Yeah there are a lot of examples of dates being written two ways on the same document/artifact. In the Anglosphere there are two changes that happened close together: the movement of the new year from Lady Day to the first of January, and the Julian/Gregorian calendar jump, so that confounds things slightly. https://en.wikipedia.org/wiki/Old_Style_and_New_Style_dates

The proper name for the calendar using the Gregorian system before the start of the Gregorian calendar is "the proleptic Gregorian calendar".

And indeed that's Python's calendar:

'A date object represents a date (year, month and day) in an idealized calendar, the current Gregorian calendar indefinitely extended in both directions.'

'This matches the definition of the “proleptic Gregorian” calendar in Dershowitz and Reingold’s book Calendrical Calculations.'

https://docs.python.org/3/library/datetime.html#id2 https://docs.python.org/3/library/datetime.html#id5

Whereas Ruby has proleptic Gregorian Time, but civic DateTime:

https://ruby-doc.org/stdlib-2.6.1/libdoc/date/rdoc/DateTime....

Think it depends on usage? Taking October 1st and 20th, and you want to know how many days passed, what's the right answer? If it's days lived, you would want the answer to not be 20, as some of those days didn't happen. But in some other context (perhaps something transitioning to the calendar earlier), they did?

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