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Re: 1-0.95

From Marko Rauhamaa <marko@pacujo.net>
Newsgroups comp.lang.python
Subject Re: 1-0.95
Date 2014-07-02 23:00 +0300
Organization A noiseless patient Spider
Message-ID <878uobpm40.fsf@elektro.pacujo.net> (permalink)
References <mailman.11388.1404254753.18130.python-list@python.org> <53b424d7$0$29985$c3e8da3$5496439d@news.astraweb.com> <8761jflms2.fsf@elektro.pacujo.net> <53b4509a$0$29985$c3e8da3$5496439d@news.astraweb.com>

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Steven D'Aprano <steve+comp.lang.python@pearwood.info>:

>>    >>> Rational(2).sqrt() * Rational(2).sqrt() == Rational(2)
>>    False
>
> Square root of 2 is not a rational number.

Nobody said it was. It's just that even "arbitrary-precision" rational
numbers wouldn't free you from the issues of floating-point numbers. The
Decimal number class won't do it, either, of course.

On the other hand, floating-point numbers are perfect whenever you deal
with science and measurement. And when you deal with business (= money),
integers are the obvious choice.

I would venture to say that the real applications for Decimal are very
rare. In practice, I'm afraid, people with rather a weak understanding
of numbers and computation might gravitate toward Decimal unnecessarily.


Marko

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Thread

1-0.95 Pedro Izecksohn <izecksohn@yahoo.com> - 2014-07-01 14:17 -0700
  Re: 1-0.95 pecore@pascolo.net - 2014-07-02 01:13 +0200
  Re: 1-0.95 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-02 15:27 +0000
    Re: 1-0.95 Marko Rauhamaa <marko@pacujo.net> - 2014-07-02 19:59 +0300
      Re: 1-0.95 Skip Montanaro <skip@pobox.com> - 2014-07-02 12:34 -0500
      Re: 1-0.95 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-02 18:34 +0000
        Re: 1-0.95 Marko Rauhamaa <marko@pacujo.net> - 2014-07-02 23:00 +0300
          Re: 1-0.95 Chris Angelico <rosuav@gmail.com> - 2014-07-03 10:16 +1000
          Re: 1-0.95 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-03 02:19 +0000
            Re: 1-0.95 Rustom Mody <rustompmody@gmail.com> - 2014-07-02 21:06 -0700
              Re: 1-0.95 Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-07-03 16:55 +1200
                Re: 1-0.95 Rustom Mody <rustompmody@gmail.com> - 2014-07-02 22:21 -0700
                Re: 1-0.95 Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-02 23:50 -0600
              OT: speeds (physical, not computing) [was Re: 1-0.95] Steven D'Aprano <steve@pearwood.info> - 2014-07-03 09:15 +0000
            Re: 1-0.95 Marko Rauhamaa <marko@pacujo.net> - 2014-07-03 09:51 +0300
              Re: 1-0.95 Steven D'Aprano <steve@pearwood.info> - 2014-07-03 09:36 +0000
                Re: 1-0.95 Marko Rauhamaa <marko@pacujo.net> - 2014-07-03 14:17 +0300

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