[Zope] summary information using ZPT

[Steve Jibson]

We've been using DTML for a few years now, but we have come to a point 
where we will be re-writing much of our zope content so I thought it 
would be a good time to look into ZPT.  I've been converting a couple of 
our DTML pages to ZPT as an exercize (or "spike solution") to determine 
if we should make the switch.  Anyway, I've run into a question that I 
can't seem to find an answer to in the docs.

If I have something like this:

<dtml-in "stuffAboutPeople()">
   <dtml-var lastName> <dtml-var age><br>
   <dtml-if sequence_last>
     Number of people: <dtml-var count-lastName><br>
     Total of ages: <dtml-var total-age><br>
     Std deviation of ages: <dtml-var standard-deviation-age><br>
   </dtml-if>
</dtml-in>


I understand how to get the repeating names and ages using ZPT, but what 
  I can't figure out is how to get the total of the ages and the 
standard deviation of the ages.

I guess the real question is: "How do I provide data that is available 
via the batch summary features in dtml-in,  using ZPT?"

Thanks!

Steve