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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 output_story_prefixes(self):
 """ Writes the set of prefixes to a file this is useful for pretty printing in results.latex_output. """


        if not self.test_story:
            raise NotImplementedError(
                "I want to write the prefixes to a file"
                "called <test_story>_prefixes.txt, but there's no test_story.")

        fn = os.path.join(TGT_DIR, "%s_prefixes.txt" % self.test_story)
        with open(fn, "w") as f:
            for utter_id in self.test_prefixes:
                print(utter_id.split("/")[1], file=f)