How do I integrate an application in the sound menu using python?

Documentation for integrating with the sound menu can be found here. Information on MPRIS is also useful if you want your application to integrate properly.

If you need help you can post to the ayatana-dev mailing list or #ayatana IRC on freenode.

Since you are looking for a python version, you might be interested in this implementation for exaile.

I'm hoping you mean to "plug into" the current sound indicator applet. if you are designing a media player (like rhythmbox or banshee) then you need to look at the following which is needed to display your media information in the sound indiactor.

http://en.wikipedia.org/wiki/Media_Player_Remote_Interfacing_Specification