Re: NaN

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From	Grant Edwards <invalid@invalid.invalid>
Newsgroups	comp.lang.python
Subject	Re: NaN
Date	Thu, 28 Apr 2011 20:39:51 +0000 (UTC)
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On 2011-04-28, Chris Rebert <clp2@rebertia.com> wrote:

>> 2. What are the use cases for NaN?  Looks like it gets used a lot as a
>> numeric (float?) object with non-value.
>
> FWICT, it's useful in lower-level languages (which typically lack
> exceptions and often lack nice ways of returning multiple values from
> a function) as a convenient way of signaling a mathematical error.

When doing stuff involving process control systems, I found it very
useful to use NaN to indicate "unknown/invalid".  It propogates
properly through calculations so that when you have an invalid input,
all of the outputs that depend on it also go invalid.

The other option is to use a value/status tuple everywhere you would
normally use a float.  But that falls over every time you need to use
a library function that expects a float as an input and returns a
float as an output.

Since the sensors return a NaN when the value is unkown/invalid it
seemed logical to continue with that paradigm in my Python code -- and
it pretty much "just works".

-- 
Grant Edwards               grant.b.edwards        Yow! If elected, Zippy
                                  at               pledges to each and every
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Re: NaN Chris Rebert <clp2@rebertia.com> - 2011-04-28 10:01 -0700
  Re: NaN Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-28 18:59 +0000
    Re: NaN Terry Reedy <tjreedy@udel.edu> - 2011-04-28 17:23 -0400
    Re: NaN Grant Edwards <invalid@invalid.invalid> - 2011-04-28 21:56 +0000
  Re: NaN Grant Edwards <invalid@invalid.invalid> - 2011-04-28 20:39 +0000

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