[Python-ideas] Quick idea: defining variables from functions that take the variable name

[Steven D'Aprano]

On Tue, Jun 07, 2016 at 11:17:26PM -0400, Eric V. Smith wrote:

> I think we might need some helpers, and a slight change to the 
> specifics. I'd have:
> 
> @binding_method
> x = obj
> 
> result in:
> x = binding_method('x', obj)

That's a bit more promising. 

Disadvantage:
- what was one line is now two;
- confusing to pass more than a single argument (plus the implicit name) 
  to the function;
- fails the principle "things that look similar should be similar".

Status quo:

    Record = namedtuple('Record', fields)

would become:

    @namedtuple
    Record = fields

which doesn't look awful. I'm sad that it needs two lines.

But what if you want to pass more than one argument?

    @namedtuple
    Record = fields, True

That will be equivalent to

    namedtuple('Record', (fields, True))

which is not what is wanted. And it gets worse if you use a keyword 
argument:

    Record = fields, verbose=True

I don't really like the way the @ syntax is being used for two 
completely different things.

    @function
    def spam(): ...

does one thing, but

   @function
   spam = ...

does a completely different and unrelated thing. I'm not saying that @ 
cannot be used for anything but decorators, but I think it is confusing 
to use something which looks so close to decorator syntax for something 
that is nothing like a decorator.


> The question for me is: do we want to have something that tells the 
> compiler that "binding_method" or "namedtuple" above are special, or is 
> this just what the compiler does for all uses of what looks like a 
> decorated assignment statement?

I'm surprised you ask that question :-) What does the Zen say about 
special cases?

I don't think it is desirable to have developers have to go cap in hand 
to the core devs and say "Please sir, I have a function that needs to 
know its name, can you please add it to the privileged list of special 
functions that work with @ please?"

*wink*

It should either work for any name after the @ or not at all. Hard 
coding support for just namedtuple would be bad.


-- 
Steve