Plistlib doesn't do much error checking, and it can crash on bad 
input. Moreover, it doesn't provide much help if it does crash (no 
linenumbers, etc).

The problem I ran into was a dangling <key>foo</key>. After this 
key the dict ended, but the next entry in the surrounding 
datastructure, an array, picked up the key from self.currentKey 
and crashed in addObject().

I was about to fix this when I noticed that there's lots of problems 
with <key> handling, duplicates or missing ones aren't detected 
either and can cause crashes too. It may be better to put a general 
try/except in parse() and print a line number or something in case 
of a failure.