[Python-ideas] Object grabbing

[Steven D'Aprano]

Hello Robert, and welcome,

On Sun, May 01, 2016 at 10:27:04PM +0200, Robert van Geel wrote:
[...]
> The idea is to be able to write this code:
> 
> myobject.a
> myobject.b
> myobject.c()
> myobject.d = 1
> 
> like this:
> 
> using myobject:
>     .a
>     .b
>     .c()
>     .d = 1

I think this is closely related to the Pascal "with" statement, which has a FAQ:

https://docs.python.org/2/faq/design.html#why-doesn-t-python-have-a-with-statement-for-attribute-assignments

You require a leading dot to access attribute names, which avoids the 
ambiguity between attributes and variables, but it also fails the "new 
syntax shouldn't look like grit on Tim's monitor" test.

using myobject:
    .method(.eggs + (.spam or ham) - tomato - .cheese)


All of these proposals raise the question, what do you do with nested 
blocks?

using myobject:
    print(.attr)
    using yourobject:
        print(.attr)


Obviously in the outer block, ".attr" refers to myobject. My guess is 
that inside the inner block, it refers to yourobject. What happens if 
you want to refer to both? Would we have to write this?

using myobject:
    print(.attr)  # myobject
    using yourobject:
        print(.attr)  # yourobject
        print(myobject.attr)  # be explicit


Now imagine that you are a beginner, trying to understand this code 
block. What would you think it does? Might you not be surprised that 
the two references to ".attr" refer to different variables?

And of course there is always the objection that the barrier to adding a 
new keyword is quite high. Somewhere out there, somebody is using 
"using" as a variable name (perhaps a decorator?) and making this a 
keyword will break her code. Is it worth it?


Despite these objections, I'm cautiously interested in this. I don't 
think the objections are insurmountable, and if there is a significant 
gain in readability and performance, it may be worth while.

A cautious and tentative +1.

It may be worth you doing a survey of other languages and seeing if they 
have anything similar.


-- 
Steve