docs: 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())