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Why does __ne__ exist?


On 2018-01-08 01:31, breamoreboy at gmail.com wrote:
> On Monday, January 8, 2018 at 12:02:09 AM UTC, Ethan Furman wrote:
>> On 01/07/2018 12:33 PM, Chris Angelico wrote:
>>> On Mon, Jan 8, 2018 at 7:13 AM, Thomas Jollans wrote:
>>>> On 07/01/18 20:55, Chris Angelico wrote:
>>>>> Under what circumstances would you want "x != y" to be different from
>>>>> "not (x == y)" ?
>>>>
>>>> In numpy, __eq__ and __ne__ do not, in general, return bools.
>>>>
>>>>>>> a = np.array([1,2,3,4])
>>>>>>> b = np.array([0,2,0,4])
>>>>>>> a == b
>>>> array([False,  True, False,  True], dtype=bool)
>>>>>>> a != b
>>>> array([ True, False,  True, False], dtype=bool)
>>>
>>> Thanks, that's the kind of example I was looking for. Though numpy
>>> doesn't drive the core language development much, so the obvious next
>>> question is: was this why __ne__ was implemented, or was there some
>>> other reason? This example shows how it can be useful, but not why it
>>> exists.
>>
>> Actually, I think it is why it exists.  If I recall correctly, the addition of the six comparative operators* was added 
>> at the behest of the scientific/numerical community.
>>
>> --
>> ~Ethan~
>>
>> * Yeah, I can't remember the cool name for those six operators at the moment.  :(
> 
> The six rich comparison methods were added to 2.1 as a result of PEP 207, which confirms that you're correct, they were added at the request of the numpyites.

Interesting sentence from that PEP:

"3. The == and != operators are not assumed to be each other's
complement (e.g. IEEE 754 floating point numbers do not satisfy this)."

Does anybody here know how IEE 754 floating point numbers need __ne__?


> 
> --
> Kindest regards.
> 
> Mark Lawrence.
>