[Zope] Flexible path generation for metal:use-macro with Python (KeyError)

[Thomas Duebendorfer]

I am looking for a flexible way to define the path for a macro to be used.

The following works:
 <span metal:use-macro="here/content_macro_main.html/macros/main | 
     here/content_macros.html/macros/main | 
     here/content_macros.html/macros/no_main_content">

It tries to locate the macro "main" first in the file
content_macro_main.html and if that fails, ZOPE tries to find it in
content_macros.html and if that fails too, the macro "no_main_content" in
content_macros.html is called.

Now, I would like to generate this sequence of alternative paths by a 
Python script to have full flexibility. Therefore I tried the following 
approach:

Create a Python "getMacroPath" script that takes the parameter "macroname" 
and looks like this:
 return 'here/content_macro_main.html/macros/' + macroname

(Of course, the script will finally generate many paths separated by "|")

In the ZOPE Page Template mydoc.html I use:
<span tal:omit-tag="" tal:define="macropath python:here.getMacroPath('main')">
 <span metal:use-macro="here/?macropath">
   <!-- main slot -->
   <H2>Welcome</H2>
   <P>We welcome you to our website.</P>
 </span>  
</span>

The Python script seems to work correctly, but ZOPE complains with 
the error:
 Error Type: KeyError
 Error Value: here/content_macro_main.html/macros/main

However, I don't see why METAL and/or ZOPE cannot deal with a TAL variable 
that has the correct value when it can deal with the same value as a 
string itself. Any ideas?


Regards,

 Thomas Duebendorfer