[Interface-dev] module-level interface

[Stephan Richter]

On Thursday 09 June 2005 02:47, John Lenton wrote:
> Thus, in interfaces.py:
>   class IWindow(Interface): pass
>   class ISkin(Interface):
>     Window = IWindow
> and in the skin:
>   class Window(Container):
>     implements(IWindow)

This does not look right to me. Interfaces can either have attributes or 
methods. In your case you have a special attribute that has the requirement 
to provide ``IWindow``. The right way to do it would be to write a 
custom/derived implementation of ``IAttribute``. Note that Zope 3 itself has 
solved this problem by providing an advanced schema package that allows you 
to describe much more meta-data of attributes using fields. Here an example:

>>> import zope.interface
>>> import zope.schema

>>> class IWindow(zope.interface.Interface):
...     pass
...
>>> class Window(object):
...     zope.interface.implements(IWindow)

>>> class ISkin(zope.interface.Interface):
...     Window = zope.schema.Object(
...         schema=IWindow,
...         title=u'Window',
...         description=u'This is the Window of the Skin',
...         required=True)

>>> class Skin(object):
...     zope.interface.implements(ISkin)
...     Window = None

>>> win = Window()
>>> skin = Skin()
>>> skin.Window = win

>>> import zope.interface.verify
>>> zope.interface.verify.verifyObject(IWindow, win)
True
>>> zope.interface.verify.verifyObject(ISkin, skin)
True

Note that this is working code. You can copy the above into a doctest and it 
will work. Since it does not matter whether the implementations are class 
instances or modules, it will work for modules as well.

Regards,
Stephan
-- 
Stephan Richter
CBU Physics & Chemistry (B.S.) / Tufts Physics (Ph.D. student)
Web2k - Web Software Design, Development and Training