Import, edit and export a Lilypond file using Python

Hello everyone,

I've asked a question on StackOverflow about Lilypond files and Python,
and someone suggested that I ask the lilypond community directly.

For the long version, you can see the question here :
http://stackoverflow.com/questions/22883594/generating-pdf-midi-from-musicxml-using-python

For the short version :
I would like to import an existing Lilypond .ly file, remove some parts
and export the resulting file as .ly/pdf/midi/mp3, using Python.
(in fact my input is a musicxml file but now I've discovered the
musicxml2ly script so that's not a problem)
What would you suggest as the most appropriate tools (probably python
libs) to do so ?

Thanks a lot,