Python autovivified nested dictionary

Vividict.py

class Vividict(dict):
    """
    dict class which allows to set deeply nested values. Any nested dict will get autovivified.
    Note that using defaultdict is more performant, so in case of huge datasets revert to that one.
    
    However using this class and not 'closing' it after setting values might result in undesired behavior:
    When accessing a value which is not set, no KeyError is thrown, instead it's autovivified into an empty Vividict.
    To guarantee this doesn't happen but KeyError is thrown, dictify() needs to be called to transform the data structure
    into regular dicts.
    
    Usage example:
      dict = Vividict()
      dict['level1']['level2'] = 'value'
      dict.dictify()
    
    See https://stackoverflow.com/questions/635483/what-is-the-best-way-to-implement-nested-dictionaries
    """
    def __missing__(self, key):
        value = self[key] = type(self)()
        return value

    def dictify(self):
        self._rec_dictify(self)

    def _rec_dictify(self, d):
        for k, v in d.iteritems():
            if isinstance(v, Vividict):
                d[k] = self.rec_dictify(v)
        return dict(d)

It throws me an error
AttributeError: 'Vividict' object has no attribute 'rec_dictify'
when I call dictify() function