[z3-five] Re: Traversal issue [was: 0.2 release]

[Philipp von Weitershausen]

Janko Hauser wrote:
> Philipp von Weitershausen wrote:
> 
> 
>>The code in Sidnei's branch raises NotFoundError now except when it
>>thinks it's being called from ZPT pathexpressions; then it returns None.
>>As explained above, this is not correct behaviour. I suggested to solve
>>the issue by implementing the following:
>>
>>- __bobo_traverse__ always raises AttributeError when it cannot
>>traverse. This seems to be the overall expected behaviour.
>>
>>- for the ZPublisher, we don't want AttributeError showing but NotFound.
>>To achieve this, we wrap __bobo_traverse__ in a descriptor that does the
>>funky frame introspection and converts AttributeErrors into NotFound.
>>That way the magic is at least contained in that descriptor.
>>
>>Objections?
>>
> 
> I saw your remark on irc, do you think this would work with
> ExtensionClass based objects? To overwrite this later in some classes
> these need to be new_style?

Yes. I was confusing simple method descriptors with the fancy 'property' 
descriptor. 'property' only works on new-style classes. Standard 
descriptors are quite simple. The one I'm suggesting would look like this:


def ZPublisherCompatibleTraverser(meth):
     def func(self, REQUEST, name):
         # XXX do some actual inspecting here
         if calledFromZPublisher:
             try:
                 return meth(self, REQUEST, name)
             except (AttributeError, KeyError):
                 return REQUEST.RESPONSE.notFoundError(name)
         else:
             return meth(self, REQUEST, name)
     return func


Then Products.Five.traversable.Traversable would look like:


class Traversable:

     def __fallback_traverse(self, REQUEST, name):
         raise AttributeError, name

     __fallback_traverse__ = 
ZPublisherCompatibleTraverser(__fallback_traverse__)



This way Traversable.__fallback_traverse__ is a regular function object 
(the 'func' function from inside ZPublisherCompatibleTraverser). Since 
it doesn't matter whether you have an UnboundMethodType or a 
FunctionType on a class and ExtensionClasses allow us to monkey with 
them anyway, it should work :)

Maybe Sidnei can take this code and add his frame magic where I put the 
comment and then check it into his branch. Then we'll know for sure.

Philipp