[Python-ideas] datetime: Support infinity
steve at pearwood.info
Mon Jan 26 12:44:40 CET 2015
On Mon, Jan 26, 2015 at 10:14:23AM +0100, Antoine Pitrou wrote:
> On Mon, 26 Jan 2015 09:24:07 +0100
> Thomas Güttler <guettliml at thomas-guettler.de> wrote:
> > PostgreSQL can store the representation of an “infinite” date, timestamp, or interval. Infinite dates are not available
> > to Python, so these objects are mapped to date.max, datetime.max, interval.max. Unfortunately the mapping cannot be
> > bidirectional so these dates will be stored back into the database with their values, such as 9999-12-31.
> Unless someone has a real-world use for the values of date.max,
> datetime.max, interval.max, I find it rather counter-productive to not
> store them back as infinities.
That would make them de-facto infinities that weirdly don't look like
datetime.date(9999, 12, 31)
If I'm reading this page correctly, PostgreSQL supports a lot of dates
that Python doesn't, up to 5874897AD:
so it might not matter if 9999-12-31 gets turned into infinity rather
than treated as a normal date.
> Adding infinities to the datetime module would probably be possible but
> someone has to figure out the arithmetic rules. Do we need "not a time"
> when adding infinity to -infinity?
I shouldn't think so. The purpose of NANs in IEEE-754 maths is to allow
the programmer to delay dealing with the failed operation until the end
of the calculation. I don't think that date calculations tend to be
anywhere as complicated as mathematical ones, so it would be acceptable
to just raise an exception.
Besides, Postgresql doesn't have a "NotATime" value, so if we're trying
to match what they do, we don't need one either.
More information about the Python-ideas