A dict that automatically creates values for missing keys. This is the same as collections.defaultdict in the Python standard library. It's provided here for Python 2.4, which doesn't have that class.
When you try to read a key that's missing, I call missing_func without args to create a value. The result is inserted into the dict and returned. Many Python type constructors can be used as missing_func. Passing list or set creates an empty dict or set. Passing int creates the integer 0. These are useful in the following ways:
>> d = defaultdict(list); d[ANYTHING].append(SOMEVALUE) >> d = defaultdict(set); d[ANYTHING].include(SOMEVALUE) >> d = defaultdict(int); d[ANYTHING] += 1