Session and validate_request()

Hi again,
it seems like I'm in trouble again:)
lets imagine I have modular random session application,
and initialize session variables in main script (specified as start_page
script in application
constructor) in validate_request() method.
I hoped that validate_request() called on each request.
The problem: if user have no actions for a while, session is dead
because of session timeout.
And if user try to request after dead session any page he gets an
exception, because of session is dead,
and no session variables any more. So he got no variable exception
trace.

The way to avoid this is to put check of session
variables existence in each .py module, but this is brute force method.
Is any smart solution already exists for this kind of problem?

thanks in advance,
denis