float("nan") in set or as key

[Jerry Hill]

> On Wed, Jun 1, 2011 at 1:30 PM, Carl Banks <pavlovevidence at gmail.com> wrote:
> True, but why should the "non-integer number" type be floating point
> rather than (say) rational?

You seem to be implying that python only provides a single non-integer
numeric type.  That's not true.  Python ships with a bunch of
different numeric types, including a rational type.  Off the top of my
head, we have:

IEEE floating point numbers
(http://docs.python.org/library/stdtypes.html#numeric-types-int-float-long-complex)
Rationals (http://docs.python.org/library/fractions.html)
Base-10 fixed and floating point numbers
(http://docs.python.org/library/decimal.html)
Complex numbers
(http://docs.python.org/library/stdtypes.html#numeric-types-int-float-long-complex
plus http://docs.python.org/library/cmath.html)
Integers (both ints and longs, which are pretty well unified by now)

Floats have far and away the best performance in most common
situations, so they end up being the default, but if you want to use
something different, it's usually not hard to do.

-- 
Jerry