On 29/05/2011 15:41, Grant Edwards wrote:
On 2011-05-29, Wolfgang Rohdewald<wolfg...@rohdewald.de> wrote:
On Sonntag 29 Mai 2011, Tim Delaney wrote:
There's a second part the mystery - sets and dictionaries (and
I think lists) assume that identify implies equality (hence
the second result). This was recently discussed on
python-dev, and the decision was to leave things as-is.
On Sonntag 29 Mai 2011, Grant Edwards wrote:
Even if they are the same nan, it's still not equal to itself.
if I understand this thread correctly, they are not equal to itself
as specified by IEEE
And Python follows that convention.
but Python treats them equal in sets and dictionaries for performance
reasons
It treats them as identical (not sure if that's the right word). The
implementation is checking for ( A is B or A == B ). Presumably, the
assumpting being that all objects are equal to themselves. That
assumption is not true for NaN objects, so the buggy behavior is
observed.
Would there be any advantage to making NaN a singleton? I'm thinking
that it could make checking for it cheaper in the implementation of
sets and dicts. Or making NaN unhashable?
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