[Zope-dev] traversal: different with and without a request

[Marius Gedminas]

On Wed, Oct 15, 2008 at 06:02:55PM +0200, Philipp von Weitershausen wrote:
> Christian Theune wrote:
> > we stumbled over an annoyance that took a while to debug:
> > 
> > Writing an ITraversable, we used zope.traversing.api.traverse() in a
> > test to verify our code. We registered the ITraversable as an
> > (non-multi) adapter and ended up with a working test.
> > 
> > In the actual system, we found that the traversable would not be used.
> > After investigation we found a conditional branch in the traverse()
> > function which would look for a multi-adapter if a request was around,
> > and a regular adapter if not.
> > 
> > We didn't anticipate this difference and it cost us some time, so we
> > wonder whether this has to be the way it is, or whether this could be
> > changed to behave more obvious and consistent.
> 
> zope.traversing is a mess.

You can drop the ".traversing" bit and it'll still be true.

On the other hand Perl is a mess, yet it is quite successful.

> First of all, its name is quite misleading. It should really be called 
> 'zope.resolvepath' because it resolves TALES-like object paths. In fact, 
> it's pretty much only used by the PageTemplate machinery to hook it up 
> to the TALES engine (with one exception, see below). The request 
> shouldn't really be necessary for this kind of path resolution, I think. 
>   The conditional multi-adaption sounds like a DWIM feature that I would 
> consider one of our many mistakes that we made in the beginnings of our 
> using the Component Architecture.
> 
> There is a process that actually needs the request and this process is 
> what I call traversal: breaking down a URL and finding a publishable 
> object.

I've seen these two called object traversal and URL traversal
respectively.

> zope.traversing has (almost) nothing to do with it, the real 
> kind of traversal happens in the publisher and facilitates 
> IPublishTraverse adapters (rather than ITraversable). The only case when 
> the two kinds of "traversal" are intermingled is when ++namespaces++ are 
> involved. Then IPublishTraverse-style traversal uses ITraversable 
> adapters. This has long been considered a mistake but was never fixed.
> 
> I'm not sure my explanation are helpful ;). Did I mention it was a mess?

Marius Gedminas
-- 
Please do not even think about automatically normalizing file names
anywhere. There is absolutely no need for introducing such nonsense, and
deviating from the POSIX requirement that filenames be opaque byte
strings is a Bad Idea[TM] (also known as NTFS).
	-- Markus Kuhn
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