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This is starting to come up a lot more as people switch from pytz to zoneinfo, so a reminder about datetime arithmetic semantics; addition is NOT referring to elapsed time:
https://blog.ganssle.io/articles/2018/02/aware-datetime-arithmetic.html
(Relevant SO question: https://stackoverflow.com/q/64440016/467366 )
To be honest, I feel like I may have shot myself in the foot by trying to get the word out about this the last few years. It's so widely misunderstood that I may have been able to make the case for a backwards-incompatible change based on "we'd be fixing more code than we break".