[XML-SIG] DOM Considered Harmful :-)

Jim Fulton jim@digicool.com
Wed, 05 May 1999 17:11:18 -0400

Greg Stein wrote:
> On Wed, 5 May 1999, Jim Fulton wrote:
> > > I'm tremendously in favor of the model returned by qp_xml.
> >
> > (BTW, could you provide a link to this proposal?
> > I must have deleted the message that contained it.  I'd
> > like to look at it.)
> It's available from my page at: http://www.lyra.org/greg/

Thanks, I'll take a look.

> > Acquisition has worked very well in Zope.  It provides a
> > very nice way to share information in a containment hierarchy.
> > It's only drawback is that it requires use of ExtensionClass,
> > which is actually a bonus. ;)
> :-)
> Is that still a patch to the interpreter, or is it all Python code now?

It never was a patch.  It *is* an extension module. There's an ExtensionClass 
extension module and an Acquisition axtension module, which requires 
the ExtensionClass extension to be around.
> I'd be interested to see what kinds of changes would be needed to use the
> acquisition stuff.

Basically, you subclass one of the acquisition base classes
(Explicit or Implict) and then, when you want to refer to a parent
in a child (that has been accesses through a parent), you refer
to the parent via the attribute, aq_parent.  

Given that in DOM (if my vague recollection serves me :) children are
not accessed as attributes, the access methods need to return the children
on the context of the parent, as in:

 import Acquisition

 class MyClass(Acquisition.Explicit):

   def some_method_that_returns_a_child(self, ... whatever):
        return theChild.__of__(self)

The special method __of__, which comes from a mix-in class
returns one object "in the context of" another.


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