[Python-Dev] Mixing float and Decimal -- thread reboot

Steven D'Aprano steve at pearwood.info
Thu Mar 25 11:18:42 CET 2010

On Thu, 25 Mar 2010 05:26:12 am Alexander Belopolsky wrote:
> Mark, I wonder if you could describe an algorithm off the top of your
> head that relies on NaN == NaN being false.

I don't know whether "relies on" is appropriate, but consider:

def myfunc(x, y):
    if x == y:
        return 1.0
        return something_complicated**(x-y)

Optimising floating point code is fraught with dangers (the above fails 
for x=y=INF as well as NAN) but anything that make Not A Numbers 
pretend to be numbers is a bad thing.

I'd like to turn the question around ... what algorithms are there that 
rely on NaN == NaN being True?

Steven D'Aprano

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