NestedDict

gistfile1.py

class NestedDict(dict):
    def __getitem__(self, key):
        if key in self: return self.get(key)
        return self.setdefault(key, NestedDict())
        
        #http://ohuiginn.net/mt/2010/07/nested_dictionaries_in_python.html retrieved 2014-05-09
        #Credit (and thanks) to Dan O'Huiginn
        #could also use __missing__ instead:
 
 class NestedDict(dict):   
    def __missing__(self, key):
        value = self[key] = type(self)()
        return value

#arguably cleaner, but doesn't prettyprint nicely
Tree = lambda: defaultdict(Tree)
t = Tree()