float("nan") in set or as key

[Chris Angelico]

On Wed, Jun 1, 2011 at 12:59 PM, Carl Banks <pavlovevidence at gmail.com> wrote:
> On Sunday, May 29, 2011 7:53:59 PM UTC-7, Chris Angelico wrote:
>> Okay, here's a question. The Python 'float' value - is it meant to be
>> "a Python representation of an IEEE double-precision floating point
>> value", or "a Python representation of a real number"?
>
> The former.  Unlike the case with integers, there is no way that I know of to represent an abstract real number on a digital computer.

This seems peculiar. Normally Python seeks to define its data types in
the abstract and then leave the concrete up to the various
implementations - note, for instance, how Python 3 has dispensed with
'int' vs 'long' and just made a single 'int' type that can hold any
integer. Does this mean that an implementation of Python on hardware
that has some other type of floating point must simulate IEEE
double-precision in all its nuances?

I'm glad I don't often need floating point numbers. They can be so annoying!

Chris Angelico