This function allows traversals over several keys to
        be performed by passing a list of keys::

            d.chained_get(key1,key2,key3) = d[key1][key2][key3]

def chained_get(self, *keys):
        """
        This function allows traversals over several keys to
        be performed by passing a list of keys::

            d.chained_get(key1,key2,key3) = d[key1][key2][key3]

        """
        existing = self
        for i in range(0, len(keys)):
            if keys[i] in existing:
                existing = existing[keys[i]]
            else:
                return None
        return existing