What purpose does a python backend serve?
A "Python backend" is simply server-side software written in Python, no different in general terms than server-side software written in PHP.  It does all the same things, just with a different programming language.
I am primarily a PHP developer, and I have been browsing the source code of a few open-source applications recently(Mozilla Bespin in particular), to find that some of them use a Python "back-end."  I was just wondering what the purpose of this back-end is.  I am assuming it is the same thing as the model in an MVC framework and is used to interface with the database, but I'm unsure.  If I'm right and the back-end is used to simply interface with the database, is the sqlite/mysql server included in the backend, because I didn't see any database config information in the install directions?