[Python-Dev] Multiple dicts for string interpolation?

[Jim Fulton]

Ken Manheimer wrote:
> 
> On Tue, 25 Jan 2000, Skip Montanaro wrote:
> 
> >     Guido> Skip:
> >     >> I'd like to propose a third alternative.  How about if the string
> >     >> interpolation function accepted a tuple of dictionaries directly:
> >     >>
> >     >> s = format % (d1, d2)
> > [...]
> >     Guido> I think it depends on to what extent this is a common, useful
> >     Guido> idiom.  Do you have evidence of that?  Examples?
> >
> > Well, the first place I ran into it was in DocumentTemplates a few years
> > ago.  They used an idiom heavily which may have now been replaced by
> > acquisition where you'd effectively push and pop value dicts onto a stack as
> > you entered and exited nested blocks of DTML code.  Their solution was a
> > special dict-like object.
> 
> Implementation of acquisition basically uses a MultiDict underneath.

No it doesn't.  Acquisition achieves combination of multiple 
namespaces in much the same way that inheritence does (through
delagation).

> Consider acquisition as a cumulative context composed from the containers
> of the target of a web request.  (Actually, a distinction is made between
> the object containment hierarchy of the target and the successive
> components of the path along which the target is reached by the request,
> with the containment contexts taking precedence - but that's probably not
> important here:-)  Add in incidental things like the server environment
> (from which you can get HTTP_REFERER and cookies and so forth).  Each of
> the components can be a dictionary or a MultiDict (or a sequence of pairs,
> i think), and they're ultimately composed in a MultiDict.
> 
> I think another place in zope where multidicts play prominently is in the
> security mechanism, where any object can have local roles, and the
> ultimate role of a user within a context is composed from the union across
> the containment hierarchy.  There probably are lots of other places where
> multidicts are used.

Acquisition plays a role in security, but MultiDicts-like things are 
not used.
 
> Suffice to say that there's a lot of composing of contexts that goes on in
> Zope in general, acquistion being a prime example but not the only one,
> and multidicts play heavily in many.  I would be surprised if this need to
> combine contexts is peculiar to web server, or general server
> applications.
> 
> > [...]
> > It's not a big deal.  If it seems too obscure the other obvious solutions
> > are not gruesome.
> 
> I suppose we'd be pretty happy to have something like MultiDict as part of
> python...

Note that Zope actually uses two separate flavors. The one used most
in Zope (in DocumentTemplate) has very specific hooks to work with
Zope's security machinery.

Jim

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