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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 label(self, id):
 """ return label for a subject id Will make use of both the ontology and the association set """

        if self.ontology is not None:
            label = self.ontology.label(id)
            if label is not None:
                return label
        if self.subject_label_map is not None and id in self.subject_label_map:
            return self.subject_label_map[id]
        return None