This is useful for setting nested dictionaries and setting items like objects

AutoVivifaction.py

class AutoVivification(dict):
    """
    Implementation of perl's autovivification feature.
    
    >>> a = AutoVivification()
    >>> a[1][2][3] = 4
    >>> a[1][3][3] = 5
    >>> a[1][2]['test'] = 6
    >>> print a
    >>> {1: {2: {'test': 6, 3: 4}, 3: {3: 5}}}

    """
    def __getitem__(self, item):
        try:
            return dict.__getitem__(self, item)
        except KeyError:
            value = self[item] = type(self)()
            return value