Re: dynamic, metaclasses and Virtual properties

        Hi Erny and all,

On Wed, 30 Jun 2004, Ernesto Revilla <[email protected]> wrote:
[original post can be found at:
 https://sf.net/mailarchive/forum.php?thread_id=5035017&forum_id=10674]

> I think that Python has a design error with properties, but it is easy to
> correct this. 
[demonstration that properties aint behaving very good when it comes to
 inheritance]
> In Modeling, when inheriting from class created with properties (dynamic), it
> does NOT the inherited methods. Is this reasonable?

You're right, this needs some attention, really.  Could you submit this
as a bug report or as a patch proposal @sf.net please?

> Here I have attached a
> little patch for dynamic.py. I made a local function mkProp, so that variable
> binding is correct, otherwise  it does not work the way it should.

Can you be more explicit on this point?

> Just a
> remark about the setter. As in the original code, a virtual setter is created
> only if the attribute is settable in the base class. In this case, we have two
> alternatives: 1. do not create a setter, as the original code, 2. create
> always a virtual setter and the setter in the base class raises a
> ReadOnlyAttributeException. (This is was I have done in a experimental
> framework.)

For the moment being we're not handling any 'readOnly' properties on
attributes --and the one in entity is still ignored for now, so I can't
really see whazt your point is, I suspect I'm misunderstanding something
here.

  Oh, and BTW sorry for taking such a long time to answer :/

-- Sébastien.


> Index: dynamic.py
> ===================================================================
> RCS file: /cvsroot/modeling/ProjectModeling/Modeling/dynamic.py,v
> retrieving revision 1.1
> diff -u -r1.1 dynamic.py
> --- dynamic.py	16 Feb 2004 20:01:06 -0000	1.1
> +++ dynamic.py	30 Jun 2004 16:07:47 -0000
> @@ -144,10 +144,16 @@
>  def add_properties(aClass, entity):
>    for p in entity.classProperties():
>      #print 'defining prop: ', p.name()
> -    part_func_name=capitalizeFirstLetter(p.name())
> -    prop=property(getattr(aClass, 'get'+part_func_name),
> -                  getattr(aClass, 'set'+part_func_name), None)
> -    setattr(aClass, p.name(), prop)
> +    part_func_name=capitalizeFirstLetter(p.name())
> +    readonly=not hasattr(aClass,'set'+part_func_name)
> +    def mkProp(name, readonly=0):
> +        getter=lambda s: getattr(s,'get'+name)()
> +        if readonly:
> +            setter=None
> +        else:
> +            setter=lambda s, v: getattr(s,'set'+name)(v)
> +        return property(getter, setter)
> +    setattr(aClass, p.name(), mkProp(part_func_name, readonly))
>      
>  def build(model, define_properties=0):
>    module_name=model.packageName()



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