[Python-ideas] PEP 505: None-aware operators

[Brendan Barnwell]

On 2018-07-19 11:43, Elazar wrote:
>
> On Thu, Jul 19, 2018 at 11:37 AM Brendan Barnwell <brenbarn at brenbarn.net
> <mailto:brenbarn at brenbarn.net>> wrote:
>
>
>              As far as I can see, these null-coalescing operators would
>     break that
>     model.  The PEP doesn't seem to provide for a "real" magic method
>     allowing users to override the actual behavior of the method.  (You can
>     only override __has_value__ to hook into it, but not define by fiat
>     what
>     A ?? B does, as you can with other operators.)  And I think the reason
>     for this is that the operator itself is too specific, much more
>     specific
>     in semantics than other operators.  (I had similar doubts about adding
>     the matrix-multiplication operator @.)
>
>
> It is just as specific as the `is` operator, and for the same reason.

	What reason is that?

	The "is" operator is the ONLY operator that is un-overridable in this 
way, and that's because by its nature it is concerned with object 
identity, which we don't want people to be able to redefine.  (Okay, the 
logical operators like "and" and "or" are also un-overridable, but 
that's not because we don't want people to be able to override them, 
it's because it's hard to figure out a way to do it practically without 
giving up short-circuiting.)

	From my perspective "A if A is None else B" is just not remotely close 
to being as special as "A is B".  If we didn't have the "is" operator 
there would be no way to do what it does.  Everything that these new 
operators do can already be done.

-- 
Brendan Barnwell
"Do not follow where the path may lead.  Go, instead, where there is no 
path, and leave a trail."
    --author unknown