On 2022-04-17 02:46:38 +1000, Chris Angelico wrote: > On Sun, 17 Apr 2022 at 02:45, Peter J. Holzer <hjp-pyt...@hjp.at> wrote: > > On 2022-04-17 02:14:44 +1000, Chris Angelico wrote: > > > So which one is it? Which one do you get when you add days=7 to a > > > datetime? > > > > For adding a datetime and timedelta I think the answer is clear. > > But subtracting two datetimes is ambiguous. > > > > But if the difference between two datetimes is a timedelta, then > surely adding a timedelta to a datetime should give the other > datetime?
Not necessarily. You might compute the difference for another purpose.
If you compute a change rate from two gauge readings you would compute
something like (r1 - r0) / (t1 - t0). You don't intend to add (t1 - t0)
to any timestamp, so that property would be irrelevant. However, you do
want something which can be used in a division and which has a
consistent unit (so one could argue that you don't want a timedelta
object at all, but a floating point number).
hp
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