[TransWarp] State of Transwarp

Steve Alexander steve at cat-box.net
Wed Jun 12 18:17:01 EDT 2002

Phillip J. Eby wrote:
> Recent work on Zope 3 has evolved the state-of-the-art 
> in Python "proxy" objects, and Zope 3 implements security proxies 
> already.  What I'm curious about is how well non-security-related 
> proxies would play in the Zope 3 model, since a lot of Zope code 
> requests the removal of proxies in order to inspect objects or to bypass 
> security.  Obviously, that's not a JAC problem; it's just something I'm 
> curious about in the Z3 architecture.

Most of the total unwrapping that goes on in Zope 3 happens to objects 
that represent Elements: the "data" or "business" objects of the 

One case when they are always unwrapped is before being added to a 
persistent container.

There are two kinds of proxies in Zope 3: context wrappers and security 
proxies. Jim has a vision of security proxies only being used where 
absolutely necessary, so with any luck, there will be a body of trusted 
code where you won't see many security proxies.

Context wrappers are used to record the traversal path to an object so 
that service lookups can follow that path back. In certain cases, a 
context wrapper needs to rebind the "self" of a method call to be the 
contextwrapper rather then the original self. This rebinding could be 
considered a pointcut operation. It is implemented conditionally on the 
type of the attribute descriptor.


Methods that strip off the proxies of an object usually also keep around 
the original wrapped object, because they need the services of security 
wrappers or context wrappers. The unwrapped object is only used where 
we're sure we want an unwrapped object.

I think that a pointcut wrapper would work well enough with Zope 3. The 
ContextWrapper implementation is designed to be subclassed, and in fact 
has been to provide the method rebinding.
Of course, there are performance considerations for such method 
rebinding. I'm pretty certain that TransWarp's fresh classes will 
execute faster than subclasses of ContextWrapper implemented in Python. 
The C implementation is pretty fast though.

Steve Alexander

More information about the PEAK mailing list