I have a python script used to send email to people,
but don't want to email people more than once. I currently use a Python
Starting from GAE 1.7.4, GQL supports
SELECT DISTINCT ... queries so you could use that to get back the set of ... well ... distinct email address for your customers.
Please note that modern (how much modern?) versions of GQL have support for the
GROUP BY clause too, if that suits your needs best.