Why does __ne__ exist?

[Thomas Nyberg]

On 01/08/2018 03:25 PM, Oren Ben-Kiki wrote:
> I am hard pressed to think of a case where __ne__ is actually useful.

Assuming you're talking about a case specifically for IEEE 754, I'm
starting to agree. In general, however, it certainly is useful for some
numpy objects (as mentioned elsewhere in this thread).

> That said, while it is true you only need one of (__eq__, __ne__), you
> could make the same claim about (__lt__, __ge__) and (__le__, __gt__).
> That is, in principle you could get by with only (__eq__, __le__, and
> __ge__) or, if you prefer, (__ne__, __lt__, __gt__), or any other
> combination you prefer.

This isn't true for IEEE 754. For example:

>>> float('nan') < 0
False
>>> float('nan') > 0
False
>>> float('nan') == 0
False

Also there are many cases where you don't have a < b OR a >= b. For
example, subsets don't follow this.

> "Trade-offs... trafe-offs as far as the eye can see" ;-)

Yes few things in life are free. :)