[Python-ideas] Operator as first class citizens -- like in scala -- or yet another new operator?

[Yanghao Hua]

On Sun, May 26, 2019 at 10:25 PM Chris Angelico <rosuav at gmail.com> wrote:
>
> On Mon, May 27, 2019 at 6:05 AM Yanghao Hua <yanghao.py at gmail.com> wrote:
> > Doesn't matter how it ends up, I
> > urge the python community do give it a second thought. (Don't you guys
> > think it is odd that Python can overrides almost every operation but
> > not for assignment ... is assignment really worthy being a special
> > case?!)
>
> Yes. It IS a special case, because assignment is not handled by the
> object being assigned to. When you assign to an attribute or subscript
> of an object, the *parent* object determines how the assignment is
> done, not the one being replaced. Look at languages where the
> being-replaced object gets to redefine assignment (C++ and PHP come to
> mind, and there may be others). MANY MANY parts of your code become
> harder to comprehend. It's not the only thing special enough to be
> non-overridable. In Python, you have several fundamentals that are
> absolutely guaranteed:
>
> a = b
> a is b
> b if a else c
> a or b # a and b
>
> There is no way that the values of a, b, or c can change the meanings
> of these expressions. (The truthiness of 'a' will define which of two
> options is chosen, but you cannot redefine the operator itself.)
>
> This is a Good Thing.

Absolutely right and good. But if you just had := or <== mean
"assignment behavior is handover to the object if __assign__ is
defined", then you can remove the whole descriptors thing (or rather,
it can do all a descriptor can and better, and actually := or <== is
saying, hey look, I am a descriptor ... ) . ;-)

I am not saying "=" should be overloaded, I am saying there should be
an assignment that can be overloaded, which completes the picture in
python.