[Zope] I Got the Concatenation Blues

[Ben Ocean]

Hi;
I've built a site with inline frames. Each page has one inline frame that 
bears the same name as the page calling it with the tag *_frame*. I want to 
code into my template a way to call the dtml document and render it within 
a noframes tag in the calling document. I have created a Python method 
called concatFrame.py:

import string

def concatFrame(str):
  frame = string.join(str,'_frame')
  return frame

I'm trying to call it thusly:

<dtml-var "concatFrame(title_or_id())">

It ain't working. What do I need to do?
TIA,
BenO