Routinely deleting aged postgresql rows via cron
A method that I find useful is to implement the cleanup code in my main programming framework (so Django, I guess, in your case) and expose that function via a URL. Then in my crontab I use wget or curl to invoke the cleanup URL.  That way the cron file is only responsible for the scheduling part, while the code that does the cleanup is kept together with the code that creates the data that needs to be cleaned up.