Chris Withers wrote:
Hi All,

I saw the zope.proxies module and wondered if it might be able to help me with two problems I need to solve:

- can these proxies be used to keep track of a traversal path in much the same way (although no seperate containment and context chains needed) as the old Zope 2 acquisition wrappers did?

We generally assign a __parent__ attribute to objects that have a hierarchical parent object. Objects have to explicitly allow this by providing ILocation (or the derived IContained). If they're not ok with having __parent__ assigned, we wrap them in a persistent containment proxy [1]. It will make the original object behave normally, except for the ILocation/IContained API (__parent__, __name__ attributes). It will intercept those values and store them inside the pickled proxy. THat way the object won't ever see the __parent__ attribute assigned to itself.

- once a proxy has been created, the the object it's proxying for be replaced?

I don't understand this question.

You'll have to explicitly do the wrapping and then continue to work with the wrapped object. Container implementations use the following kind of code in __setitem__ [2]:

    if not IContained.providedBy(object):
        if ILocation.providedBy(object):
            zope.interface.alsoProvides(object, IContained)
        else:
            object = ContainedProxy(object)

and then they add 'object' to their datastructure (e.g. a BTree) and assign object.__parent__ and object.__name__.


[1] zope.app.container.contained.ContainedProxy
[2] zope.app.container.contained.containedEvent
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