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[Python-Dev] == on object tests identity in 3.x

Stephen J. Turnbull stephen at xemacs.org
Tue Jul 8 09:53:50 CEST 2014 
Chris Angelico writes:

 > The reason NaN isn't equal to itself is because there are X bit
 > patterns representing NaN, but an infinite number of possible
 > non-numbers that could result from a calculation.

I understand that.  But you're missing at least two alternatives that
involve raising on some calculations involving NaN, as well as the
fact that forcing inequality of two NaNs produced by equivalent
calculations is arguably just as wrong as allowing equality of two
NaNs produced by the different calculations.  That's where things get
fuzzy for me -- in Python I would expect that preserving invariants
would be more important than computational efficiency, but evidently
it's not.  I assume that I would have a better grasp on why Python
chose to go this way rather than that if I understood IEEE 754 better.
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