On 3 Apr 2006 10:37:11 -0400 in comp.lang.python, [EMAIL PROTECTED] (Roy
Smith) wrote:
>Adam DePrince <[EMAIL PROTECTED]> wrote:
>> It just happens that the
>>logical operation
>>
>> (a is b ) -> (a == b )
>>
>>is always True.
>
>Only for small values of "always". You can always do pathological
>things with operators:
>
>class Foo:
> def __eq__ (self, other):
> return False
>
>f = Foo()
>print f is f
>print f == f
>
>frame:play$ ./is.py
>True
>False
>
>This may even be useful. What if you were trying to emulate SQL's
>NULL? NULL compares false to anything, even itself. To test for
>NULLness, you have to use the special "is NULL" operator.
Another instance where this may be useful is IEEE-754 NaN. I don't
have fpconst to verify if that's the case, but I would expect
NaN is NaN to be true, but NaN == NaN to be false.
Regards,
-=Dave
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