[Python-Dev] Python-Dev Digest, Vol 69, Issue 143

[Mark Dickinson]

On Fri, Apr 17, 2009 at 3:58 PM, Scott David Daniels
<Scott.Daniels at acm.org> wrote:
> Non-associativity is what makes for floating point headaches.
> To my knowledge, floating point is at least commutative.

Well, mostly. :-)

>>> from decimal import Decimal
>>> x, y = Decimal('NaN123'), Decimal('-NaN456')
>>> x + y
Decimal('NaN123')
>>> y + x
Decimal('-NaN456')

Similar effects can happen with regular IEEE 754 binary doubles,
but Python doesn't expose NaN payloads or signs, so we don't
see those effects witihin Python.

Mark