[Python-Dev] PEP 318 - generality of list; restrictions on elements

[Guido van Rossum]

> > So decorators couldn't be used to create read-only properties?
> 
> Maybe I'm misunderstanding something.  I thought that a property
> contains a get descriptor, which makes it a kind of callable.

That's irrelevant; the property itself isn't callable.

> Also, I thought we had explicitly punted on allowing decorators to
> create properties because the syntax wasn't sufficiently flexible
> without contortions.

It would work just fine for read-only descriptors; in fact I believe
that

   def foo [property] (self):
       return ...calculated value of foo...

would be all you need (it would be nice if property tried to get the
docstring out of the get function).

In any case, *I* would prefer not to let the semantics require
anything, and to make this just a (preferred) shorthand for applying
arbitrary transformations to something that starts out as a function.

Two additional thoughts:

1) I'm not sure I like using the same syntax for classes; the use
   cases are so different that using similar syntax only adds
   confusion, and I think the use cases for classes are a lot weaker
   than for methods.

2) The syntax should also apply to regular functions.

3) It needs to be crystal clear that the list of transformations is
   applied at function/method definition time, not at class definition
   time (which is later, after all the methods have been collected in
   a namespace).

--Guido van Rossum (home page: http://www.python.org/~guido/)