[Zope-dev] Re: more __call__ ...

[Jim Fulton]

Chris Withers wrote:
> 
> (moving back onto list, hopefully my head/wall contact will save others
> braincells ;-)
> 
> Jim Fulton wrote:
> > > On an (almost) related matter, are there any docs (other than the code
> > > ;-) for how __call__ is handles WRT to <dtml-var something>?
> > > I had a look at DTMLMethod.py and PythonMethod.py and ended up very
> > > confused...
> >
> > Currently, DTML looks at something that it is going to render
> > and tries to decide if it's callable. If it is, it checks to
> > see if it has a true isDocTemp attribute. If an object is callable
> > and has a true isDocTemp, then it is called with None and the DTML
> > namespace. Otherwise, if an object is callable, it is just called.
> 
> So, if I give my product a class attribute of isDocTemp=1, what
> signature should I give my product's __call__ method so it picks up the
> DTML namespace?

  def __call__(self, ignored, md): ...

> > We are going to provide an alternate interface, so that if
> > an object has a special method, then this will be called instead.
> 
> okay... which proposal/project is this in?

I don't remember. Evan?
 
> > > I think the 'client', rather than 'self' is what I'm after, but how can
> > > I get it inside my product's __call__ method?
> 
> Hmmm... I don't suppose there's a nice definition of what the 'client'
> is, what's likely to be in the namespace stack and what self is likely
> to be in these circumstances lying around anywhere, is there? ;-)
  
client is just a namespace, defined by it's attributes. It's not really
in the namespace. Neither is self.
 
> > You can't really.  You should be able to infer it from the acquisition
> > context. For example, 'client' should be aq_parent.
> 
>     def __call__(self):
>         """ """
>         print self.aq_parent.id
> 
> This is called by a <dtml-var myObject> in standard_html_header which is
> also called with a dtml-var in, lets say, the DTML documnet: myDocument.
> 
> The above code prints the id of this product instance's container.

That's what I expect. 'client', in DocumentTemplate is usually
the object the template was invoked on.

> I was
> expecting it to print the id of myDocument. Is this me misunderstanding
> what the 'client' is,

Yes.

> or is something else going on?
> 
> In either case, what do I need to go to get hold of what would be
> PARENTS[0-1], if you see what I mean?

I don't see what you mean.  
 
> > Note that subtemplates
> > are not invoked on the objects they are found in, but in the namespace
> > they are called in. This is a bit weird and not really intensional. :(
> 
> I think I'm probably going to be relying on this, and I _think_ it makes
> sense to me. I presume subtemplate calls are things like doing <dtml-var
> myObject>?

That's fine.

> In which case it seems sensible to keep playing in the
> namespace and just popping myObject on top as an instanceDict. I'm note
> quite sure how you think this area should work adn what difference it
> would make, could you elaborate? :-S

First, I have no intention of changing anything in a backward
incompatible way. For that matter, I don't have much interest in
changing DTML at this point, given:

http://dev.zope.org/Wikis/DevSite/Projects/XHTMLTemplate

I think that if you say:

  <dtml-var expr="foo.bar">

that foo's namespace should take precedence over
the DTML namespace, but, in fact, foo's namespace
is ignored. I think that this should at least
happen optionally.  Otherwise, how could you think
of bar as a method?

 
> > > PS: In python product terms, whats' the difference between implementing
> > > __call__, __str__ or render?
> >
> > render?
> 
> Yeah, that's what I thought, but a coupla people have mentioned it.
> Maybe they're thinking of DTML tags?

Well, a number of people have suggested that there should
be a separate render (ie call as subtemlpate) interface. 
Maybe that's what what you meant.

Evan, help me out here. :)
 
> > __call__ implements the () operator (in C++ terms). It is the method
> > you implement to make your object callable.
> >
> > __str__ is the method you implement to control how your object is
> > converted to a human readable string.
> 
> So what's the difference in terms of doing <dtml-var myobject> and
> http://site.com/myobject, if there is any?

The difference is clearer if you have 

  http://site.com/foo/bar

vs 

  <dtml-var expr="foo.bar">

in http://site.com/zoo/splat.

In the former case, foo's namespace is 
at the top of the stack and, in the second case, 
it's not on the stack.

> PS: What I'm actually looking for out of all of this is the
> getPhysicalPath() of the final object that was traversed through the
> URL.
> e.g: If the URL was http://www.nipltd.com/folder/somethingelse/myobject,
> I'm looking for something like:
> [<Application Instance at 0x000000> (Zope) , <Folder Instance at
> 0x000000> (folder) , <DTMLDocument Instance at 0x000000> (myobject)]

getPhysicalPath returns a list of strings, not objects.
 
> If there's an easier way to get this from within the __call__ method of
> a python product, someone PLEASE tell me! ;-)

aq_chain(x, 1)[-1:] should give this to you, I believe, or
be very close. :)

Jim

--
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