Python dot-equals (syntax proposal)

[Steven D'Aprano]

On Sun, 02 May 2010 17:09:36 +1000, Lie Ryan wrote:

> On 05/02/10 10:58, Steven D'Aprano wrote:
>> On Sun, 02 May 2010 05:08:53 +1000, Lie Ryan wrote:
>> 
>>> > On 05/01/10 11:16, Steven D'Aprano wrote:
>>>> >> On Fri, 30 Apr 2010 12:34:34 -0400, D'Arcy J.M. Cain wrote:
>>>> >> 
>>>> >> In practice though, I think that's a difference that makes no
>>>> >> difference. It walks like an operator, it swims like an operator,
>>>> >> and it quacks like an operator.
>>>> >> 
>>>> >> 
>>> > Nope it's not. A full-time operator in python have a reflected
>>> > version (e.g. __radd__), which dot does not have.
>> What are the reflected versions of __eq__ and __ne__ (binary == and !=
>> operators)?
> 
> Python do not have them now, but it does make sense if python have
> them[1]. OTOH, given current python's language semantic, __rgetattr__
> doesn't make any sense; adding __rgetattr__ would require a quite
> fundamental change to the language's semantic, primarily how attribute
> resolution works.
> 
> [1] though they'd probably be dismissed as bad idea since equality and
> inequality are supposed to be a symmetric relation; reflected
> (in)equality makes it way too easy to break that premise
> 
>> And __neg__, __pos__ and __inv__ (for the unary - + and ~ operators)?
>> 
>> And the three-argument form of __pow__ for power(1, 2, x)?
> 
> I know you're a famed nitpicker, but don't be silly, reflected operator,
> by definition, only makes sense for binary operator.

Binary operators aren't the only kind of operator, and you claimed that:

"A full-time operator in python have a reflected version".

But there are full-time operators that don't have reflected versions, so 
your claim is just *wrong*. It would still be wrong even if you had 
limited yourself to binary operators.

I have agreed with you that there are useful things people might want to 
do (e.g. function composition) that you can't do because the "dot 
operator" isn't a *real* operator with exactly the same semantics as 
"plus operator", "multiply operator" and friends. I think we're in 
violent agreement, and merely disagreeing over semantics. There's no need 
to continue arguing against a position I haven't actually taken :)


-- 
Steven