[Alex] >> For me, subtraction in this case is similar to conversion. Fix the EPOCH >> and d = t - EPOCH together with t = EPOCH + d gives you a bijection between >> times and timedeltas.
[Tim] > Well, not without more words to clarify which operations are intended. > For example, it's impossible to tell what "-" means there unless you > spell out whether you're using classic or timeline arithmetic. In > order to make your final claim true, I have to (I believe) > reverse-engineer that the claim is restricted to naive EPOCH and `d`, > or aware datetimes in a common fixed-offset zone. Otherwise your "-" > uses timeline arithmetic and your "+" classic arithmetic, and they're > different kinds of arithmetic in a non-fixed-offset zone. I'm missing a case there: common non-fixed-offset zone. That one doesn't fail because different kinds of arithmetic are used (classic is always used then), but because classic arithmetic ignores `fold` entirely - there's no bijection in that case if you're viewing `t` as civil time. So, your EPOCH and ` t` share a common (possibly None) tzinfo, and you're talking about a bijection in naive (not civil) time. _______________________________________________ Datetime-SIG mailing list [email protected] https://mail.python.org/mailman/listinfo/datetime-sig The PSF Code of Conduct applies to this mailing list: https://www.python.org/psf/codeofconduct/
