[Python-ideas] Decorators for variables

[Ian Kelly]

On Fri, Apr 1, 2016 at 8:18 AM, Matthias welp <boekewurm at gmail.com> wrote:
> Currently the way to create variables with custom get/set/deleters is to use
> the @property decorator or use property(get, set, del, doc?), and this must
> be repeated per variable. If I were able to decorate multiple properties
> with decorators like @not_none or something similar, it would take away a
> lot of currently used confusing code.

I don't see the relationship between this paragraph and the rest of
your proposal. How does a decorator in place of an explicit function
call prevent repetition?

> I propose the following syntax, essentially equal to the syntax of function
> decorators:
>
>     @decorator
>     var = some_value
>
> which would be the same as
>
>     var = decorator(some_value)
>
> and can be chained as well:
>
>     @decorator
>     @decorator_2
>     var = some_value
>
> which would be
>
>    var = decorator(decorator_2(some_value))
>
> or similarly
>
>     var = decorator(decorator_2())
>     var = some_value

What about augmented assignment? Should this work?

@float
var += 20

And would that be equivalent to:

@float
var = var + 20

Or:

var = var + float(20)

Also, what about attributes and items?

@decorator
x.attr = value

@another_decorator
d['foo'] = value

> The main idea behind the proposal is that you can use the decorator as a
> standardized way to create variables that have the same behaviour, instead
> of havng to do that using methods. I think that a lot can be gained by
> specifying a decorator that can decorate variables or properties.

By "methods" you mean "function composition", right? Otherwise I don't
understand what methods have got to do with this.