looking for template package

[Neal Becker]

I'm looking for something to do template processing.  That is, transform 
text making various substitutions.  I'd like to be able to do substitutions 
that include python expressions, to do arithmetic computations within 
substitutions.

I know there are lots of template packages, but most seem aimed at web use.  
This is just text processing, not part of any web stuff.

Any suggestions?