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Message from discussion a.index(float('nan')) fails
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Terry Reedy  
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 More options Oct 26 2012, 3:54 am
Newsgroups: comp.lang.python
From: Terry Reedy <tjre...@udel.edu>
Date: Fri, 26 Oct 2012 03:54:02 -0400
Local: Fri, Oct 26 2012 3:54 am
Subject: Re: a.index(float('nan')) fails
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On 10/25/2012 10:44 PM, Steven D'Aprano wrote:

> On Thu, 25 Oct 2012 22:04:52 -0400, Terry Reedy wrote:

>> It is a consequence of the following, which some people (but not all)
>> believe is mandated by the IEEE standard.

>>   >>> nan = float('nan')
>>   >>> nan is nan
>> True

> The IEEE 754 standard says nothing about object identity. It only
> discusses value equality.

>>   >>> nan == nan
>> False

> IEEE 754 states that all NANs compare unequal to everything, including
> NANs with the same bit value. It doesn't make an exception for
> comparisons with itself.

> I'm not entirely sure why you suggest that there is an argument about
> what IEEE 754 says about NANs.

I did not do so.

> As far as I can see, the argument is
> whether or not language designers should pick and choose which bits of
> the standard they want to follow, thus taking a step backwards to the
> chaos of numerical computing prior to the IEEE 754 standard.

There has been disagreement about whether the standard mandates that
Python behave the way it does. That is a fact, but I have no interest in
discussing the issue.

--
Terry Jan Reedy


 
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