For our processing of bibliographic records with Python, one of the more useful classes we've developed is something we call flat files. A flat file has a very simple structure. It is composed of lines separated by line feeds, and each line is a key-value pair, separated by a tab. The keys are required to be unique and sorted. A very simple format, but like Python dictionaries, very useful.
We use this structure for loading our authority files into memory for processing. The whole file is read in as a single string, and then a binary-chop is used to find the data associated with a particular key (well, actually we do a little more than that now).