Confused about file caching

Hi,

I am using apache 1.3.34 with mod_python 2.7.11 on Debian Etch.

I have a request that parses, modifies and saves an XML file. A
subsequent request reopens the file for reading but it is sometimes
(not always) getting what seems to be a cached copy of the file
instead of the one that was recently modified and saved.

What component is the more likely to be doing the caching, apache,
mod_python or the OS, and how would I go along disabling them
individually?

Thanks in advance,
Alex