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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 getSubgraphList(self, parent_name):
 """Returns list of names of subgraphs for Root Graph with name parent_name. @param parent_name: Name of Root Graph. @return: List of subgraph names. """

        if not self.isMultigraph:
            raise AttributeError("Simple Munin Plugins cannot have subgraphs.")
        if self._graphDict.has_key(parent_name):
            return self._subgraphNames[parent_name] or []
        else:
            raise AttributeError("Invalid parent graph name %s."
                                 % (parent_name,))