1. Dates beyond year 9999 aren't a prerequisite for infinite types - I see
that as a separate issue. The fact that we can't represent dates between
9999 and infinity doesn't make infinity less useful :)
2 & 3. Yeah, string representation is something that needs to be decided on
- that's a big potential bikeshed. My preference at this stage would be for
these to be called e.g. date.inf_future and date.inf_past, and the string
representation to be the same. timedelta could simply
have timedelta.infinity, and since it supports __neg__, -timedelta.infinity
would work just fine. I'd like to hear other views though.
4. In my implementation, `datetime.now() - DATETIME_NEG_INF ==
TIMEDELTA_POS_INF`. I haven't implemented the division dunder methods yet,
but by analogy to float, I would say that `TIMEDELTA_POS_INF /
timedelta(days=1) == float("inf")` and `TIMEDELTA_POS_INF //
timedelta(days=1)` raises TypeError (the latter returns nan in the case of
float).
Thanks,
Alex
On Wed, Jun 17, 2020 at 2:57 PM Serhiy Storchaka <storch...@gmail.com>
wrote:
> 16.06.20 13:54, Alexander Hill пише:
> > I’d like to propose support for infinite dates, datetimes and
> > timedeltas. They're very useful when you need to model ranges with one
> > or both ends unbounded (e.g. “forever starting from June 15th 2020”).
> >
> > Without first-class infinite values, you can use None, or you can use
> > the `min` and `max` attributes of Python’s datetime types, or some other
> > arbitrary large values. Using None means you need to implement a path
> > for None, and a path for everything else, and your various infinite
> > values are indistinguishable. Using max/min means comparisons just work,
> > but calculations need special treatment and you’re fundamentally
> > misrepresenting your meaning.
> >
> > Temporal infinities give the best of both worlds: infinite values that
> > interoperate seamlessly with the built-in types and behave sensibly and
> > predictably. They’re also supported by Postgres!
>
> First we need to solve some problems.
>
> 1. Parsing dates with more than 4-digit year. Note that many external
> implementations do not support such data, so we need a way to restrict
> the data range when convert them to string representation.
>
> 2. String representations and parsing for negative data.
>
> 3. String representations and parsing for infinity data (positive and
> negative).
>
> 4. If datetime.min will be the negative infinity, then what will be the
> result of `datetime.now() - datetime.min`? Or `(datetime.now() -
> datetime.min) // timedelta(days=1)`?
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