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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 extend_with(self, rdf_file):
 """Extend the RDF graph of this HierarchyManager with another RDF file. Parameters rdf_file : str An RDF file which is parsed such that the current graph and the graph described by the file are merged. """

        self.graph.parse(os.path.abspath(rdf_file), format='nt')
        self.initialize()