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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 paths(self):
 """Iterates through all files in the set"""

        if self.format is None:
            raise ArcanaFileFormatError(
                "Cannot get paths of fileset ({}) that hasn't had its format "
                "set".format(self))
        if self.format.directory:
            return chain(*((op.join(root, f) for f in files)
                           for root, _, files in os.walk(self.path)))
        else:
            return chain([self.path], self.aux_files.values())