[Python-ideas] Why is nan != nan?
rhamph at gmail.com
Fri Mar 26 03:26:28 CET 2010
On Thu, Mar 25, 2010 at 20:01, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> So we have three correctness-preserving possibilites:
> 1) Always raise an exception as soon as a NaN is
> 2) Propagate NaNs through arithmetic but raise an
> exception when attempting to compare them.
This forces you to explicitly compare them when desired, but it's even
simpler than I realized (and doesn't require new functions).
def func(a, b):
if not isnan(a) and not isnan(b) and a == b:
All it requires is you check for NaN before your normal comparison.
It's even backwards compatible with Python 2.6!
If that example is a little verbose for you, just make isnan take
multiple arguments and return true if any are NaN.
> 3) Return a NaB when comparing NaNs, and raise an
> exception when attempting to branch on a NaB.
Adam Olsen, aka Rhamphoryncus
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