Re: Floating point "g" format not stripping trailing zeros

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From	Grant Edwards <invalid@invalid.invalid>
Newsgroups	comp.lang.python
Subject	Re: Floating point "g" format not stripping trailing zeros
Date	Fri, 13 Feb 2015 20:33:16 +0000 (UTC)
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On 2015-02-13, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Fri, Feb 13, 2015 at 7:02 AM, Grant Edwards <invalid@invalid.invalid> wrote:
>> On 2015-02-12, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>> On Thu, Feb 12, 2015 at 1:23 PM, Hrvoje Nikšić <hniksic@gmail.com> wrote:
>>>
>>>> {:.15g} is supposed to give 15 digits of precision, but with trailing
>>>> zeros removed.
>>>
>>> The doc says with "insignificant" trailing zeros removed, not all
>>> trailing zeros.
>>
>> Can somebody explain the difference between "significant" and
>> "insignificant" tailing zeros to somebody who barely passed his single
>> numerical methods class?  [Though I have, on occasion, had to tinker
>> with the innards of SW floating point libraries and could fish a
>> hardcopy of IEEE-754 out of a filing cabinet if needed.]
>
> Significant digits are within the precision of the calculation.
> Writing 1.230 indicates that the fourth digit is known to be zero.
> Writing 1.23 outside a context of exact calculation indicates that the
> fourth digit is unknown due to insufficient precision.

I knew that, but I was asking in the context of float/decimal's
formatting function.  I didn't realize that float and/or decimal had a
"significant digit" property, and therefore possess significant vs.
insignificant trailing zeros when represented in base-10.

-- 
Grant Edwards               grant.b.edwards        Yow! Mr and Mrs PED, can I
                                  at               borrow 26.7% of the RAYON
                              gmail.com            TEXTILE production of the
                                                   INDONESIAN archipelago?

Thread

Re: Floating point "g" format not stripping trailing zeros Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-12 16:46 -0700
  Re: Floating point "g" format not stripping trailing zeros Grant Edwards <invalid@invalid.invalid> - 2015-02-13 14:02 +0000
    Re: Floating point "g" format not stripping trailing zeros Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-13 09:56 -0700
      Re: Floating point "g" format not stripping trailing zeros Grant Edwards <invalid@invalid.invalid> - 2015-02-13 20:33 +0000
        Re: Floating point "g" format not stripping trailing zeros Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-13 14:01 -0700
        Re: Floating point "g" format not stripping trailing zeros Dave Angel <davea@davea.name> - 2015-02-13 16:15 -0500
          Re: Floating point "g" format not stripping trailing zeros Grant Edwards <invalid@invalid.invalid> - 2015-02-13 21:22 +0000
            Re: Floating point "g" format not stripping trailing zeros Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-13 14:40 -0700
            Re: Floating point "g" format not stripping trailing zeros Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-13 14:49 -0700

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