[Python-ideas] Fix some special cases in Fractions?

[Neil Girdhar]

On Thu, Aug 30, 2018 at 9:03 AM Steven D'Aprano <steve at pearwood.info> wrote:

> On Wed, Aug 29, 2018 at 09:39:05PM -0700, Neil Girdhar wrote:
>
> > Would there be any problem with changing:
> >
> > In [4]: Fraction(1, 1) ** Fraction(2, 3)
> > Out[4]: 1.0
> >
> > In [5]: Fraction(-1, 1) ** Fraction(2, 3)
> > Out[5]: (-0.4999999999999998+0.8660254037844387j)
> >
> > In [6]: Fraction(0, 1) ** Fraction(2, 3)
> > Out[6]: 0.0
> >
> > I'd like these to be Fraction(1), Fraction(1), and Fraction(0).
>
> If anyone else has mentioned the backward-compatibility issue by now, I
> haven't see it. I believe that would make it a fairly big problem.
>
>
I don't think it's that big a problem since Fraction < numbers.Real


> I expect that there is code out in the wild which (for good or ill) now
> expects 1**Fraction(2, 3) to return 1.0, rather than Fraction(1), and
> similarly for the other examples. Changing that could break people's
> code.
>
> Even if we had consensus that this was a good idea, or at least
> consensus from the maths-folk who care about this sort of thing (I'd
> like to know what Uncle Timmy and Mark think of this idea), it would
> still probably need a "__future__" import to activate it, or a
> deprecation period. Or some other annoyance.
>
> Possibly the simpler approach would be to add a subclass that does what
> you want. UnitRootFraction or something.
>
> Then the only argument will be whether such a subclass ought to go into
> the fractions module, or your own personal toolkit :-)
>
> I must admit though, I'm a bit curious as to what you are doing that
> having 1**Fraction(2,3) return 1.0 is an annoyance, but having
> 27**Fraction(2,3) return 8.999999999999998 instead of Fraction(9) isn't.
>
> You're right, it would have been better in my example (linked above) to
support all of those things.

>
>
> --
> Steve
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/
>
> --
>
> ---
> You received this message because you are subscribed to a topic in the
> Google Groups "python-ideas" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/python-ideas/aZIHpPhe0mw/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> python-ideas+unsubscribe at googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20180831/c05bcbfd/attachment-0001.html>