Ah, I see. Now I admit I am confused as hell.
Code:
git clone git://github.com/kovidgoyal/calibre.git
cd calibre/src
CALIBRE_DEVELOP_FROM=`pwd`
vim calibre/__init__.py # insert print("Hello, world!") somewhere near the top
calibredb
should print "Hello, world!" Right? But it does not. I guess I am missing something very obvious:-(.