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
>> 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.
>> * 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.