[Zope-dev] Re: ComputedAttribute

5 Jan 2001

      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.