[Python-Dev] Mixing float and Decimal -- thread reboot (original) (raw)

Alexander Belopolsky alexander.belopolsky at gmail.com
Wed Mar 24 19:26:12 CET 2010

On Wed, Mar 24, 2010 at 1:39 PM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote: ..

IMO, their least useful feature is the property of being not equal to themselves -- that causes more problems than it solves because it impairs a programmer's ability to reason about their programs.

I agree. An often cited rationale for IEEE 754 behavior is that it eliminates branching in some high performance numerical algorithms. While this is likely to be true, I have never seen it benefiting real life applications, certainly not those written in Python.

I wonder why Python did not follow Java model where Float NaN objects unlike raw float NaNs compare equal to themselves. One reason may be that Python does not have raw floats, but if someone needs IEEE 754 NaNs, one can use numpy scalars or add arithmetics to ctypes numerical types.

Mark, I wonder if you could describe an algorithm off the top of your head that relies on NaN == NaN being false.

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