[Python-Dev] Definining properties - a use case for class decorators?

[Greg Ewing]

Guido van Rossum wrote:

> Nick, and everybody else trying to find a "solution" for this
> "problem", please don't.

Denying that there's a problem isn't going to make it
go away. Many people, including me, have the feeling that
the standard way of defining properties at the moment leaves
something to be desired, for all the same reasons that have
led to @-decorators.

However, I agree that trying to keep the accessor method
names out of the class namespace isn't necessary, and may
not even be desirable. The way I'm defining properties in
PyGUI at the moment looks like this:

   class C:

     foo = overridable_property('foo', "The foo property")

     def get_foo(self):
       ...

     def set_foo(self, x):
       ...

This has the advantage that the accessor methods can be
overridden in subclasses with the expected effect. This
is particularly important in PyGUI, where I have a generic
class definition which establishes the valid properties
and their docstrings, and implementation subclasses for
different platforms which supply the accessor methods.

The only wart is the necessity of mentioning the property
name twice, once on the lhs and once as an argument.
I haven't thought of a good solution to that, yet.

-- 
Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg.ewing at canterbury.ac.nz	   +--------------------------------------+