I partially got it. It's needed to add an extension referencing the org.python.pydev.pydev_pyedit_listener we then associate to this listener a class
public class MyPyEditListener implements IPyEditListener, IPyEditListener3{}
in this class we will have the following method:
@Override
public void onSave(BaseEditor arg0, IProgressMonitor arg1) {
System.console().writer().println("=== YaY: onSave");
}
Now I only need a extension to get the right python files according to the imports found in some file... Need to look, looking good :D