test for nan

[Peter Maas]

Peter Otten wrote:
>>def isNaN(x):
>>     return (x == x) == False
> 
> 
> That is not portable:
> 
> Python 2.3.3 (#1, Jan  3 2004, 13:57:08)
> [GCC 3.2] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> 
>>>>nan = float("nan")
>>>>nan != nan
> 
> False

Thanks for correction. I firmly believed that NaN != NaN -> True
was a property of IEEE 754 and of all software using this standard.
For gcc/Linux you could use

def isNaN(x):
     return (x == 0) and (x == 1)

and utilize sys.platform. :)

Mit freundlichen Gruessen,

Peter Maas

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