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

[Steven D'Aprano]

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 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.



-- 
Steve