If we wanted to be mathematically correct, taking a 4th root should give you 4 answers. You could return a tuple of (4, -4, 4j, -4j) for a 4th root of 256. It actually makes power to a Fraction(2, 4) unequal with a Fraction(1, 2) calculating this way. (which, from what I can tell, is exactly your point - don't just take a power and a square root for a fractional power, reduce it to a float or whatever first to get well-defined behaviour. )
But full mathematical correctness is probably not what we want either. Current behaviour IMO is the only solution that returns only 1 answer but does something sensible in all cases. Op za 1 sep. 2018 om 20:35 schreef Jonathan Fine <jfine2...@gmail.com>: > Greg Ewing and Jonathan Goble wrote > > >> Also, Fraction(1) for the second case would be flat-out wrong. > > > How? Raising something to the 2/3 power means squaring it and then taking > > the cube root of it. -1 squared is 1, and the cube root of 1 is 1. Or am > I > > having a 2:30am brain fart? > > Let's see. What about computing the Fraction(2, 4) power by first > squaring and then taking the fourth root. Let's start with (-16). > Square to get +256. And then the fourth root is +4. I've just followed > process Jonathan G suggested, without noticing that Fraction(2, 4) is > equal to Fraction(1, 2). > > But Fraction(1, 2) is the square root. And -16 requires complex > numbers for its square root. The problem, I think, may not be doing > something sensible in any particular case. Rather, it could be doing > something sensible and coherent in all cases. A bit like trying to fit > a carpet that is cut to the wrong size for the room. > > -- > Jonathan > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
_______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
