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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def governor(self, dep_type, node):
 """ Registers a node as governing this node :param dep_type: The dependency type :type dep_type: str :param node: :return: self, provides fluent interface :rtype: corenlp_xml.dependencies.DependencyNode """

        self._governors[dep_type] = self._governors.get(dep_type, []) + [node]
        return self