When is min(a, b) != min(b, a)?

[Pete Forman]

Mark Dickinson <dickinsm at gmail.com> writes:

 > Any change to Python that made == and != checks involving NaNs raise
 > an exception would have to consider the consequences for set, dict,
 > list membership testing.
>
>
 > and if Python had separate operators for these two purposes it
 > wouldn't be Python any more.

There are separate Python operators, "==" and "is".

The C99 standard, which Python defers to for its implementation, says
in 6.2.6.1.4: Two values (other than NaNs) with the same object
representation compare equal, but values that compare equal may have
different object representations.

In 7.12.13, the fmax and fmin functions treat NaNs as missing
arguments.  Most other operations return NaN if an argument is NaN, or
for a domain error.

7.12.14 specifies comparison macros that are quiet versions of the
relational operators.

BTW floating-point exceptions in C and IEEE are not the same as
exceptions in higher level languages.  The behavior of signalling NaNs
are not defined in C.  Only quiet NaNs are returned from operations.
An invalid floating-point exception may well just set a status flag.
That may be tested after a set of calculations.  With pipelining the
exact cause of the exception will be unknown.
-- 
Pete Forman                -./\.-  Disclaimer: This post is originated
WesternGeco                  -./\.-   by myself and does not represent
pete.forman at westerngeco.com    -./\.-   the opinion of Schlumberger or
http://petef.port5.com           -./\.-   WesternGeco.