[Zope] iterating over result sets in python

I am trying to iterate over a result set from a zsql method in a python script in Zope 2. In the results is a date field. What I want to do is test whether a date is younger than the date in the previous row by at least 30 days but I am having problems working out how, not coming from a pythonic background. Could anyone point me in the correct direction? Regards garry