[Datetime-SIG] PEP-0500 (Alternative datetime arithmetic) Was: PEP 495 ... is ready ...

Guido van Rossum guido at python.org
Tue Aug 18 06:19:33 CEST 2015

So we're writing a PEP for two people? Will they even use it?

On Monday, August 17, 2015, Tim Peters <tim.peters at gmail.com> wrote:

> [Guido]
> > Well, everyone implementing a tzinfo class will be confronted with the
> > question whether to provide those special methods or not. And they may
> well
> > be copy/pasting code that implements them. So my claim is that this makes
> > the life of everyone implementing a tzinfo a little more complex, not
> just
> > that of tzinfo implementers who actually need this protocol. Just like
> the
> > mere existence of __length_hint__ serves as a distraction for anyone
> > implementing an iterator.
> Seriously:  who writes tzinfo classes?  I do, but I don't personally
> give a rip about any form of timeline arithmetic.  Who writes
> iterators?  A better question for _that_ is "who doesn't?" ;-)
> AFAICT, only two people in over a dozen years have been serious tzinfo
> authors, and every serious I project I ever heard of uses one of their
> two packages:
> - Stuart Bishop, whose pytz wraps the Olson database, plus endures
> enormous pain to disambiguate folds.
> - Gustavo Niemeyer, whose dateutil wraps all of (at least) the Olson
> database, POSIX TZ strings, Windows registry timezones, and
> iCalendar-style VTIMEZONE files.
> Am I missing any?
> If not, who are we concerned about?  I'm pretty sure Stuart and
> Gustavo have amply demonstrated they're capable of dealing with things
> dozens of times more complex than anything discussed here.  Nobody
> else cares:  they just grab a package and use it.  That's how it
> should be.  If and when canned timezones are supplied with Python, one
> person in the core may still care - plus, of course, people highly
> motivated to do things the core doesn't cater to.
> > ...
> > That's a straw man, right? The stock markets closed around the leap
> second
> > because they can't deal with this.
> Just because I know everyone is fascinated by this ;-) , do note that
> there are many financial markets around the world, and they no more
> agree on what to do than anyone else does.  Examples for _this_ round
> of leap second include:
> - NASDAQ closed for the day early.
> - Many Asian markets opened late.
> - Many global exchanges shut down before the leap second insertion and
> opened again after the next hour passed.
> - Brazilian markets added their leap second two days early, on Sunday
> when Brazil's markets were closed.  They remained open across "the
> real" leap second insertion (which their computers' time services were
> fiddled to ignore).
> - Some markets ignored the potential problems entirely and just keep going.
> I don't know whether any problems occurred this time.  "The news" is
> great at publicizing pre-event hysteria, but poor on following up.

--Guido van Rossum (on iPad)
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