[Python-Dev] Property syntax (Re: [Python-Dev] Extended Function syntax)

[Shane Holloway (IEEE)]

Greg Ewing wrote:
 >   def foo as property:
 >     def __get__(self):
 >       ...
 >     def __set__(self, x):
 >       ...

The above syntax seems to be particularly easy to read and understand, 
and that is a Good Thing.  ;) If I understand it correctly, here is a 
longer sample::

     class Fun(object):
         def origonal(self, a, b):
             return a * b

         def foo(self, a, b) as method:
             return a + b

         def bar(klass, a, b) as classmethod:
             return klass(a, b)

         def push(self, item) as sync_method:
             self._queue.append(item)

         def pop(self) as sync_method:
             self._queue.pop()

         def circumference as property:
             """Property docstring"""
             def __get__(self):
                 return self.radius*6.283
             def __set__(self, value):
                 self.radius = value/6.283
             def __delete__(self):
                 del self.radius


Similar to Guido's behind-the-scenes implementation peak::

     def v(a0, a1, a2) as e:
         S

     T = <a thunk created from S>
     v = e(T)

     v(a0, a1, a2)
     # would be the same as
     e(T).__call__(a0, a1, a2)


Seems very clean and extensible since 'e' can interpret the thunk 'T' as 
it sees fit.  If the implementation chooses to execute the thunk and 
pull the __get__/__set__/__delete__ methods to implement a property, it 
can.  In the same way, a different implementation may choose to execute 
'T' as a code block when called, perhaps modifying the parameter list.


Issues-that-will-steal-my-sleep-tonight:
     * The scoping issues seem very hairy.
     * The definition of what the thunk is remains nebulas.
     * Additional parameters for 'e' in the 'e(T)' would be *very* useful.
     * This syntax does not address the inline semantics (and potential 
usefulness!) of Guido's proposal::

         >    foo = property:
         >        ...


Even with all these outstanding issues, the potentials start to 
tantalize the imagination!
-Shane Holloway