[Zope] Continued problem tal:condition

[KevinL]

On Fri, 2002-08-23 at 06:25, Dieter Maurer wrote:
> KevinL writes:
>  > On Thu, 2002-08-22 at 04:30, Dieter Maurer wrote:
>  > > zope writes:
>  > >  > ...
>  > >  > Now all my macros are in the same page.
>  > >  > I m am trying to use :
>  > >  >   <div tal:condition="request/form/lkid | nothing">
>  > >  >      <tal:block define="mName
>  > >  > python:here.oms.Users.lib.pset_links(lkid=request.form['lkid'])">
>  > >  >          <metal:block use-macro="container/zptmac_memall/macros/?mName">
>  > >  >           List
>  > >  >          </metal:block>
>  > > This does not work, because TAL-attributes are only evaluated once
>  > > all METAL-attributes have been executed.
>  > > 
>  > >   As a consequence you must not refer to a TAL defined variable
>  > >   in a METAL attribute.
>  > > 
>  > > Use a Python script to return the macro object you need.
>  > > 
>  > > 
>  > > Furthermore, you cannot suppress a METAL attribute execution
>  > > with a "tal:condition" (for the same reasons).
>  > > 
>  > >   Use an (almost) empty macro in such a case (it may need to
>  > >   define slots, when you call it with "metal:fill-slot").
>  > 
>  > Um.  That's wrong, I believe.
> It's explicitely stated in the documentation.
> 
> And, think a moment:
> 
>   Many tal attributes reference things available only under
>   special circumstances, e.g. form variables.
>   When you evaluate them in a different context, you will get
>   exceptions.
> 
>   Then, think of macro expansion. When macro expansion is
>   enabled, you expand macros outside when you look at the
>   template source, outside of any special context. You cannot
>   rely on tal attributes for that.
> 
>   Of course, it would be possible to not look at tal attributes
>   when macro expansion is enable but look at them when it is
>   disabled. But that would be a really strange design....
> 
> 
> Dieter
> 

I just added a page template, test_macro, and surrounded the default
content with "metal:block define-macro="test".  I added another ptl,
test, and made it consist entirely of:

<span tal:define="mName string:test">
  <metal:block use-macro="here/test_macro/macros/?mName">
  </metal:block>
</span>

When you view test, you get the test_macro macro appearing.

This works.  More than that, the conditional picking of macros like that
is important, I think - otherwise a lot of the dynamicness of a site
vanishes.  Perhaps we're talking at cross-purposes?  Or have I been
relying on a brokenness in macros/tal?  I can certainly see in the
documentation that it says macros are expanded before tal is executed,
but that seems to not be the case in practice?

KevinL