[Datetime-SIG] Calendar vs timespan calculations...

[Chris Barker]

On Thu, Jul 30, 2015 at 3:24 PM, Ethan Furman <ethan at stoneleaf.us> wrote:

> By the way -- which __add__ actually does the implementation? datetime's
>> or timedelta's ?
>>
>
> class timedelta:
>
>     def __add__(self, other):
>         if isinstance(other, timedelta):
>             # for CPython compatibility, we cannot use
>             # our __class__ here, but need a real timedelta
>             return timedelta(self._days + other._days,
>                              self._seconds + other._seconds,
>                              self._microseconds + other._microseconds)
>         return NotImplemented
>
>
> timedelta only adds directly to other timedeltas; so datetime is doing the
> actual addition.


great, thanks -- so timedelta knows nothing of datetimes at all, it seems
-- nice!

And you are quite right -- what we need a datetime with a different __add__
(and a few others, I suppose)

And it could be pretty darn backward compatible -- it would behave exactly
the same for naive datetimes, and, I think, any time zone without a DST,
and even any timezone when the DST boundary isn't crossed.

I'm thinking its "as simple" as:

- convert to utc
- convert to a timedelta from year 1
- do the addition
- convert back to a utc datetime
- convert back to the tzinfo's timezone


Or is there more to it than that that I'm missing?

-Chris





>
> --
> ~Ethan~
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