There is already class WbTime(object) with the methods above. Shouldn't we extend this class instead, with a method that accepts a pywikibot.Timestamp as input ("fromTimeStampToWbTime" or similar?)?

I completely overlooked WbTime. Shouldn't the two of them be merged into one object?

(In reply to Maarten Dammers from comment #2)

I completely overlooked WbTime. Shouldn't the two of them be merged into one
object?

Ideally yes. But I don't believe it's possible.

pywikibot.Timestamp is an extension of datetime.datetime, which has a limit on how large dates it can handle. https://docs.python.org/2.7/library/datetime.html says the year has to be between 1 and 9999, but Wikibase supports much older dates, or dates farther in the future, which is why we needed WbTime.

I think creating a fromTimeStampToWbTime or similar function is probably the best way to handle it for now.

(In reply to Mpaa from comment #1)

There is already class WbTime(object) with the methods above. Shouldn't we
extend this class instead, with a method that accepts a pywikibot.Timestamp
as input ("fromTimeStampToWbTime" or similar?)?

pywikibot.WbTime.fromTimestr(timestamp.toISOformat()) already works perfectly.

(In reply to Maarten Dammers from comment #2)

I completely overlooked WbTime. Shouldn't the two of them be merged into one
object?

Maybe, but WbTime has Wikibase-specific attributes like "precision", "after", "before" and "calendarmodel".

So I think closing this bug is okay, Does anyone disagree?

Yes, WONTFIX.