I was feeling nostalgic for the days of Apple ][ DOS 3.3 and started re-familiarizing myself with the disk layout (VTOC, catalog entries, track/sector lists, etc)
Of course, I couldn't help but then implement them in Python.
Here is a python module that reads Apple ][ DOS 3.3 disk images and can both list the disk catalog and also dump the contents of a file.
http://jtauber.com/2009/02/15/a2disk.py
Enjoy!