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Groups > comp.lang.python > #70703

Re: Significant digits in a float?

From Ben Finney <ben@benfinney.id.au>
Subject Re: Significant digits in a float?
Date 2014-04-29 13:23 +1000
References <mailman.9549.1398700831.18130.python-list@python.org> <535f0f9f$0$29965$c3e8da3$5496439d@news.astraweb.com>
Newsgroups comp.lang.python
Message-ID <mailman.9565.1398741802.18130.python-list@python.org> (permalink)

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

> By the way, you contradict yourself here. Earlier, you described 38.0 as 
> having zero decimal places (which is wrong). Here you describe it as 
> having one, which is correct, and then in a later post you describe it as 
> having zero decimal places again.

I get the impression that this is at the core of the misunderstanding.
Having a number's representation ending in “….0” does not mean zero
decimal places; it has exactly one. The value's representation contains
the digit “0” after the decimal point, but that digit is significant to
the precision of the representation.

If the problem could be stated such that “38.0” and “38” and “38.000”
are consistently described with the correct number of decimal digits of
precision (in those examples: one, zero, and three), maybe the
discussion would make more sense.

-- 
 \     “Men never do evil so completely and cheerfully as when they do |
  `\        it from religious conviction.” —Blaise Pascal (1623–1662), |
_o__)                                                   Pensées, #894. |
Ben Finney

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Thread

Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-28 12:00 -0400
  Re: Significant digits in a float? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-29 02:34 +0000
    Re: Significant digits in a float? Ben Finney <ben@benfinney.id.au> - 2014-04-29 13:23 +1000
      Re: Significant digits in a float? Steven D'Aprano <steve@pearwood.info> - 2014-04-29 05:43 +0000
        Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-04-29 20:33 -0400
          Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 20:42 -0400
            Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-04-30 20:02 -0400
              Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-04-30 22:54 -0500
                Re: Significant digits in a float? Paul Rubin <no.email@nospam.invalid> - 2014-04-30 20:56 -0700
                Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-04-30 23:16 -0500
                Re: Significant digits in a float? William Ray Wing <wrw@mac.com> - 2014-05-01 11:53 -0400
                Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-05-06 11:29 -0500
                Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-01 22:06 -0400
                Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-05-06 09:51 -0500
                Re: Significant digits in a float? alister <alister.nospam.ware@ntlworld.com> - 2014-05-06 15:18 +0000
                Re: Significant digits in a float? Joel Goldstick <joel.goldstick@gmail.com> - 2014-05-06 12:14 -0400
                Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-06 19:48 -0400
                Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-05-01 08:56 -0400
                Re: Significant digits in a float? Larry Hudson <orgnut@yahoo.com> - 2014-05-01 12:51 -0700
                Re: Significant digits in a float? Adam Funk <a24061@ducksburg.com> - 2014-05-01 22:05 +0100
                Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-01 21:47 -0400
                Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-05-06 09:59 -0500
                [OT] Silde rules [was Re: Significant digits in a float?] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-06 16:10 +0000
                Re: [OT] Silde rules Ben Finney <ben@benfinney.id.au> - 2014-05-07 10:01 +1000
              Re: Significant digits in a float? Adam Funk <a24061@ducksburg.com> - 2014-05-01 21:55 +0100
                Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-01 22:26 -0400
                Re: Significant digits in a float? Adam Funk <a24061@ducksburg.com> - 2014-05-08 20:58 +0100
    Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 09:38 -0400
      Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 02:30 +1000
        Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 19:53 -0400
          Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 10:13 +1000
          Re: Significant digits in a float? Ben Finney <ben@benfinney.id.au> - 2014-04-30 10:13 +1000
          Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 10:17 +1000
          Re: Significant digits in a float? Ben Finney <ben@benfinney.id.au> - 2014-04-30 10:20 +1000
          Re: Significant digits in a float? Grant Edwards <invalid@invalid.invalid> - 2014-04-30 18:19 +0000
      Re: Significant digits in a float? Ned Batchelder <ned@nedbatchelder.com> - 2014-04-29 12:47 -0400
        Re: Significant digits in a float? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-30 09:45 +1200
      Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 02:59 +1000
      Re: Significant digits in a float? Adam Funk <a24061@ducksburg.com> - 2014-04-29 21:16 +0100
        Re: Significant digits in a float? Mark H Harris <harrismh777@gmail.com> - 2014-04-29 15:39 -0500
          Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 07:15 +1000
        Re: Significant digits in a float? Ryan Hiebert <ryan@ryanhiebert.com> - 2014-04-29 15:42 -0500
        Re: Significant digits in a float? emile <emile@fenx.com> - 2014-04-29 15:42 -0700
          Re: Significant digits in a float? alister <alister.nospam.ware@ntlworld.com> - 2014-04-30 09:03 +0000
          Re: Significant digits in a float? Grant Edwards <invalid@invalid.invalid> - 2014-04-30 18:21 +0000
            Re: Significant digits in a float? emile <emile@fenx.com> - 2014-05-01 09:34 -0700
              Re: Significant digits in a float? alister <alister.nospam.ware@ntlworld.com> - 2014-05-01 17:13 +0000
        Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 08:51 +1000
          Re: Significant digits in a float? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-30 20:14 +1200
            Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 18:27 +1000
            Re: Significant digits in a float? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-30 14:05 +0100
        Re: Significant digits in a float? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-30 00:34 +0100
        Re: Significant digits in a float? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-04-29 20:37 -0400
        Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 20:45 -0400
        Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 10:45 +1000
          Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 20:48 -0400
        Re: Significant digits in a float? Ethan Furman <ethan@stoneleaf.us> - 2014-04-29 19:31 -0700
          Re: Significant digits in a float? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-30 02:59 +0000
            Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-29 23:30 -0400
              Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 13:40 +1000
        Re: Significant digits in a float? Chris Angelico <rosuav@gmail.com> - 2014-04-30 13:03 +1000
          Re: Significant digits in a float? Roy Smith <roy@panix.com> - 2014-04-30 08:01 -0400
        Off-topic  circumnavigating the earth in a mile or less  [was Re: Significant digits in a float?] Ethan Furman <ethan@stoneleaf.us> - 2014-04-30 06:14 -0700
        Re: Off-topic  circumnavigating the earth in a mile or less  [was Re: Significant digits in a float?] Ethan Furman <ethan@stoneleaf.us> - 2014-04-30 07:02 -0700
          Re: Off-topic  circumnavigating the earth in a mile or less Adam Funk <a24061@ducksburg.com> - 2014-05-01 21:52 +0100
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Chris Angelico <rosuav@gmail.com> - 2014-05-01 00:27 +1000
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Chris Angelico <rosuav@gmail.com> - 2014-05-01 05:10 +1000
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Ryan Hiebert <ryan@ryanhiebert.com> - 2014-04-30 10:24 -0500
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-30 17:46 -0600
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Terry Reedy <tjreedy@udel.edu> - 2014-04-30 22:20 -0400
          Re: Off-topic circumnavigating the earth in a mile or less [was Re:   Significant digits in a float?] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-05-01 18:16 +1200
          Re: Off-topic circumnavigating the earth in a mile or less Adam Funk <a24061@ducksburg.com> - 2014-05-01 21:57 +0100
            Re: Off-topic circumnavigating the earth in a mile or less Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-01 22:49 +0100
            Re: Off-topic circumnavigating the earth in a mile or less alister <alister.nospam.ware@ntlworld.com> - 2014-05-02 08:49 +0000
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Chris Angelico <rosuav@gmail.com> - 2014-05-01 11:57 +1000
        Re: Off-topic circumnavigating the earth in a mile or less [was Re: Significant digits in a float?] Vlastimil Brom <vlastimil.brom@gmail.com> - 2014-05-01 09:49 +0200
      Re: Significant digits in a float? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-30 02:50 +0000
      Re: Significant digits in a float? Grant Edwards <invalid@invalid.invalid> - 2014-04-30 18:18 +0000

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