If you want to parse AppStream files in Python you probably should just install libappstream-glib, and use the GObjectIntrospection bindings for that. AppStreamGlib is a much better library than this and handles many more kinds of component.

If AppStreamGlib is not available to you (e.g. you're trying to run in an OpenShift instance on RHEL 6.2), this project might be somewhat useful.

Contributors welcome, either adding new functionality or fixing bugs.

See also: http://www.freedesktop.org/software/appstream/docs/