The defaultdict object

In the collections module, there's a object called defaultdict. This is useful (and supposedly faster) if you were to instead call setdefault() for every insert into a regular dict.

This is especially useful for nested dicts; rather than testing for existence or calling setdefault() at every level of the dict; the following code below will run works and illustrates an example:

bidict = collections.defaultdict(dict)

bidict['a']['b'] = 1

Both levels of the dict will be initialized correctly automatically.

A more pedestrian usage might be to initialize every value to zero, which can be accomplished simply, since calling int() will always return 0:

termfreq = collections.defaultdict(int)

termfreq['unknownterm'] == 0