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
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.
On Thu, 30 Aug 2018 at 17:36, Stephan Houben wrote:
>
> I would also like to point out that the current behavior of Fraction
> is consistent with other parts of the numeric system, e.g.
> 1/1 produces 1.0 (rather than 1)
> math.sqrt(4) produces 2.0 (rather than 2)
> 1j-1j produces 0j (rather than
On Thu, Aug 30, 2018 at 9:03 AM Steven D'Aprano 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]:
Neil Girdhar wrote:
Powers of other numbers have to keep the same behavior since in general
those kinds of expressions don't create rational numbers.
There are infinitely many other rational numbers that *could*
be given the same treatment, though, e.g. (-8) ** (2/3). If
you don't want to
On 2018-08-30 00:07, Greg Ewing wrote:> Jonathan Goble wrote:
>> How? Raising something to the 2/3 power means squaring it and then
>> taking the cube root of it.
>
> On reflection, "wrong" is not quite accurate. A better
> word might be "surprising".
>
> (-1) ** (2/3) == 1 would imply that 1 **
I would also like to point out that the current behavior of Fraction
is consistent with other parts of the numeric system, e.g.
1/1 produces 1.0 (rather than 1)
math.sqrt(4) produces 2.0 (rather than 2)
1j-1j produces 0j (rather than 0.0 or 0)
So in general the type of the output is determined by
On Thu, 30 Aug 2018 at 14:06, Nicolas Rolin wrote:
> I think you could take the implementation further and decide that any
> power of Fraction(1) is Fraction(1) and any positive power of Fraction(0)
> is Fraction(0).
> I woudn't be shocked that Fraction(1) ** 3.7 == Fraction(1) and
> Fraction(0)
I think you could take the implementation further and decide that any power
of Fraction(1) is Fraction(1) and any positive power of Fraction(0) is
Fraction(0).
I woudn't be shocked that Fraction(1) ** 3.7 == Fraction(1) and Fraction(0)
** 3.7 == 0.
However the implementation for Fraction(-1)
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]: (-0.4998+0.8660254037844387j)
>
> In [6]: Fraction(0, 1) **
On Thu, 30 Aug 2018 at 12:04, Jonathan Fine wrote:
> First, the docs for the fraction module could be improved. Here's the
> page and it's history.
>
> https://docs.python.org/3/library/fractions.html
> https://github.com/python/cpython/commits/3.7/Doc/library/fractions.rst
>
> Already,
Hey, no worries. I do think though that people should feel free to suggest
ideas even if they have never contributed anything. I read python-ideas
for the discussion. Thank you for your feedback about my suggestion.
On Thu, Aug 30, 2018 at 8:18 AM Jonathan Fine wrote:
> Hi Neil
>
> When I
Hi Neil
When I wrote my previous message, I didn't know who you were, or your
previous contributions. Perhaps I should have. But I didn't.
If I had known, my remarks would have been different. In particular, I
would have acknowledged your previous contributions. I apologise for
any offence I may
;0067a655-4f82-479f-9970-5b72dc079...@googlegroups.com>
> Created on:30 August 2018 at 05:39 (Delivered after 74 seconds)
> From:Neil Girdhar
> To:python-ideas
> Subject:[Python-ideas] Fix some special cases in Fractions?
>
> Paul
>
___
u have the wrong
address for the list in your mail client?
Message ID<0067a655-4f82-479f-9970-5b72dc079...@googlegroups.com>
Created on:30 August 2018 at 05:39 (Delivered after 74 seconds)
From:Neil Girdhar
To:python-ideas
Subject:[Pytho
On Thu, Aug 30, 2018 at 7:13 AM Paul Moore wrote:
> (You're still not fixing your mail headers. Please do, it's hard to be
> bothered responding if I keep having to fix your mails in order to do
> so).
>
Sorry about that, I don't understand where it's coming from. I'm never
using google
On Thu, Aug 30, 2018 at 7:03 AM Jonathan Fine wrote:
> Hi Neil
>
> Summary: You say something should be done. But by who? Perhaps the
> should starts with you.
>
What does this mean? Are you asking who is going to do the
implementation? I posted here to get feedback about whether it would be
Thanks for the feedback.
On Thu, Aug 30, 2018 at 7:13 AM Paul Moore wrote:
> (You're still not fixing your mail headers. Please do, it's hard to be
> bothered responding if I keep having to fix your mails in order to do
> so).
>
> On Thu, 30 Aug 2018 at 11:28, Neil Girdhar wrote:
> >
> > But
(You're still not fixing your mail headers. Please do, it's hard to be
bothered responding if I keep having to fix your mails in order to do
so).
On Thu, 30 Aug 2018 at 11:28, Neil Girdhar wrote:
>
> But I'm only asking for fractional powers of -1, 0, and 1. Is that really a
> complex issue?
Hi Neil
Summary: You say something should be done. But by who? Perhaps the
should starts with you.
Warning: This has been written quickly, and might have rough edges. If
so, I apologise.
You wrote
> But I'm only asking for fractional powers of -1, 0, and 1. Is that really a
> complex issue?
On Thu, Aug 30, 2018 at 5:51 AM Nicolas Rolin
wrote:
>
>
>
>>> Right, but we already have some special cases:
>>
>> In [8]: Fraction(2, 3) ** Fraction(3, 1)
>> Out[8]: Fraction(8, 27)
>>
>> Fraction.__pow__ already tries to return Fraction objects where possible.
>>
>
>
> I think the main point
Jeroen Demeyer wrote
from sympy import Rational
Rational(1,2) ** Rational(2,3)
> 2**(1/3)/2
Rational(1,1) ** Rational(2,3)
> 1
Rational(-1,1) ** Rational(2,3)
> (-1)**(2/3)
Rational(0,1) ** Rational(2,3)
> 0
Thank you very much for this, Jeroen. Most helpful.
Perhaps
>> Right, but we already have some special cases:
>
> In [8]: Fraction(2, 3) ** Fraction(3, 1)
> Out[8]: Fraction(8, 27)
>
> Fraction.__pow__ already tries to return Fraction objects where possible.
>
I think the main point to see here is what the scope of a built-in function
should be.
For a
On Thu, Aug 30, 2018 at 5:27 AM Greg Ewing
wrote:
> Neil Girdhar wrote:
> > we want branch continuity in the power.
> > After all, floating point values have some inaccuracy, and we wouldn't
> > want chaotic behavior, i.e., small changes to the power to have drastic
> > changes to the result.
>
With gmpy2 (note that mpq=fractions, mpfr=floating-point reals):
>>> from gmpy2 import mpq
>>> mpq("1/1") ** mpq("2/3")
mpfr('1.0')
>>> mpq("-1/1") ** mpq("2/3")
mpfr('nan')
>>> mpq("0/1") ** mpq("2/3")
mpfr('0.0')
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Python-ideas mailing list
On 2018-08-30 11:11, Jonathan Fine wrote:
If anyone has time and ready access, it would help to know what
https://www.sympy.org/en/index.html does with this.
It handles such powers symbolically, not actually returning a numerical
result:
>>> from sympy import Rational
>>> Rational(1,2) **
Neil Girdhar wrote:
we want branch continuity in the power.
After all, floating point values have some inaccuracy, and we wouldn't
want chaotic behavior, i.e., small changes to the power to have drastic
changes to the result.
This is not like Fraction where we know that x ** Fraction(1, 3)
On Thu, Aug 30, 2018 at 5:11 AM Jonathan Fine wrote:
> Hi Neil
>
> We wrote
>
> >> This gives the same results as Python's Fraction, except for your
> >> example [6]. There, it gives the Fraction(0) you ask for.
> >>
> >> If the smart mathematicians and computer scientists that wrote gp/pari
>
On 2018-08-30 11:05, Jonathan Fine wrote:
I'm used to using a number theory computer algebra system
https://pari.math.u-bordeaux.fr/.
I don't think that a comparison with PARI is very relevant because PARI
doesn't really have a type system the way that Python does. For example
the fraction
Hi Neil
We wrote
>> This gives the same results as Python's Fraction, except for your
>> example [6]. There, it gives the Fraction(0) you ask for.
>>
>> If the smart mathematicians and computer scientists that wrote gp/pari
>> get the same answers, it suggests to me that improvement would be
>>
Hi Neil
You 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]: (-0.4998+0.8660254037844387j)
> In [6]: Fraction(0, 1) ** Fraction(2, 3)
> Out[6]: 0.0
> I'd like these to
On Thu, Aug 30, 2018 at 4:38 AM Stephen J. Turnbull <
turnbull.stephen...@u.tsukuba.ac.jp> wrote:
> Neil Girdhar writes:
>
> > There are a lot of misunderstandings in this thread. It's probably
> > best to start by reading up on the roots of unity (
> >
Neil Girdhar writes:
> There are a lot of misunderstandings in this thread. It's probably
> best to start by reading up on the roots of unity (
> https://en.wikipedia.org/wiki/Root_of_unity).
That's not very polite, especially in context where somebody has
already conceded that his "wrong"
On Thu, Aug 30, 2018 at 4:01 AM Paul Moore wrote:
> On Thu, 30 Aug 2018 at 08:38, Neil Girdhar wrote:
> >
> > There are a lot of misunderstandings in this thread. It's probably best
> to start by reading up on the roots of unity (
> https://en.wikipedia.org/wiki/Root_of_unity). The key ideas
Sorry if this gets double posted. Can people using Google Groups
*please* adjust the mail headers so that mailing list posters can
reply without getting errors? Ideally stop using Google Groups, but if
you have to, please consider those that don't. Specifically, please
remove the Google Groups
On Thu, 30 Aug 2018 at 08:38, Neil Girdhar wrote:
>
> There are a lot of misunderstandings in this thread. It's probably best to
> start by reading up on the roots of unity
> (https://en.wikipedia.org/wiki/Root_of_unity). The key ideas are that a real
> number has two complex square roots,
There are a lot of misunderstandings in this thread. It's probably best to
start by reading up on the roots of unity (
https://en.wikipedia.org/wiki/Root_of_unity). The key ideas are that a
real number has two complex square roots, three complex cube roots, and so
on.
Normally, in Python, we
Jonathan Goble wrote:
How? Raising something to the 2/3 power means squaring it and then
taking the cube root of it.
On reflection, "wrong" is not quite accurate. A better
word might be "surprising".
(-1) ** (2/3) == 1 would imply that 1 ** (3/2) == -1.
I suppose that could be considered true
On Thu, Aug 30, 2018 at 4:30 PM, Jonathan Goble wrote:
> On Thu, Aug 30, 2018, 2:08 AM Greg Ewing
> 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,
On Thu, Aug 30, 2018 at 2:09 AM Greg Ewing
wrote:
> Jeroen Demeyer wrote:
> > On 2018-08-30 06:39, Neil Girdhar wrote:
> >
> >> I'd like these to be Fraction(1), Fraction(1), and Fraction(0).
> >
> > Why? I cannot think of any natural use case why you would want Fractions
> > for a few special
On Thu, Aug 30, 2018, 2:08 AM Greg Ewing
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?
>
Jeroen Demeyer wrote:
On 2018-08-30 06:39, Neil Girdhar wrote:
I'd like these to be Fraction(1), Fraction(1), and Fraction(0).
Why? I cannot think of any natural use case why you would want Fractions
for a few special cases on an operation which returns non-Fractions
generically.
Also,
On 2018-08-30 06:39, Neil Girdhar wrote:
I'd like these to be Fraction(1), Fraction(1), and Fraction(0).
Why? I cannot think of any natural use case why you would want Fractions
for a few special cases on an operation which returns non-Fractions
generically.
I consider it a feature to know
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]: (-0.4998+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
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