I've gone too far this time

gistfile1.txt

import collections

def rec_dict():
    """
    Just a recursive dictionary
    """
    return collections.defaultdict(rec_dict)


class Tree(object):
    """
    A tree , automatically sets root nodes to zero [4][1] --> [4][1][0]
    """
    def __init__(self, category_dict, depth=3):
        self.tree = rec_dict()
        nested_grab = lambda keys: reduce(lambda entry, key: entry.setdefault(key, {}), [self.tree] + keys)
        for category, value in category_dict.items():
            # The filter command means that something like 1.2. or 1..2 will go to 1.2, the added zeros are to set root behavior
            actual_categories = (filter(None, category.split('.')) + ([0] * depth))
            nested_grab(actual_categories[:depth-1])[actual_categories[depth-1]] = value

categories = {
    '0'    : 'Unclassified',
    '1'    : 'Media',
    '1.1'  : 'Literature',
    '1.1.1': 'Book',
    '1.1.2': 'Author',
    '1.2'  : 'Music'
}

test = Tree(categories)

print test.tree['1']['1']['1']
>>> 'Book'