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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 _xml_for_episode_index(self, ep_ind):
 """ Helper method to retrieve the corresponding model xml string for the passed episode index. """


        # read the model xml, using the metadata stored in the attribute for this episode
        model_file = self.demo_file["data/{}".format(ep_ind)].attrs["model_file"]
        model_path = os.path.join(self.demo_path, "models", model_file)
        with open(model_path, "r") as model_f:
            model_xml = model_f.read()
        return model_xml