[Zope-dev] Re: ComputedAttribute

Fri, 5 Jan 2001 13:54:54 +0100

On Fri, Jan 05, 2001 at 12:22:32PM +0000, Chris Withers wrote:
> Martijn Pieters wrote:
> > 
> > You could use ComputedAttribute for that:
> > 
> > class MyClass(Acquisition.Explicit):
> >     # The following attribute is acquired transparently
> >     def _acquired_your_attribute(self):
> >         return self.aq_acquire('your_attribute')
> >     your_attribute = 	ComputedAttribute(_acquired_your_attribute, 1)
> > 
> >     # index_html isn't
> >     index_html = None
> 
> That looks cool :-)
> 
> Where's it documented? what does the 1 mean?

Erm. The ExtensionClass.stx documentation hints at a ComputedAttribute
class (but as an example of how you could use an ExtensionClass). The
current C implementation of ComputedAttribute is not, as far as I can see,
documented.

As for the '1', the CVS log has the following to say on that:

  Added second "level" argument for computed attributes.  This makes it
  easier to create computed attributes that work with acquisition.
  Normally, computed attributes are called with unwrapped objects. Passing
  a level of 1, causes computed attributes to be called with one level of
  wrapping.  Note that the innermost (single) level of wrapping typically
  reflects a containment context with any extra access contexts stripped
  off.

As I understand it, it makes self.aq_acquire possible.