On Sun, 17 Apr 2022 at 05:38, Peter J. Holzer <hjp-pyt...@hjp.at> wrote: > > 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: > > > 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? It's just as ambiguous. > > To answer the same question in a different way: > > No, because the timedelta object is overspecified when applied to a > specific datetime (when you start at 2022-04-16T21:29, it doesn't matter > whether you add 7 days or 168 hours) but that extra information matters > with different starting points. When you subtract two specific > datetimes, there is no way to extract that extra information. So > addition and subtraction are not symmetrical. >
Ah, that's fair. So what you're really saying is that the difference between two datetimes *isn't* a timedelta, but when we subtract them and get back a timedelta, we're throwing away information for simplicity. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
