code: def persist(self, storageLevel):
          
          if not isinstance(storageLevel, StorageLevel):
              raise TypeError("`storageLevel` should be a StorageLevel, got %s" % type(storageLevel))
          javaStorageLevel = self._java_matrix_wrapper._sc._getJavaStorageLevel(storageLevel)
          self._java_matrix_wrapper.call("persist", javaStorageLevel)
          return self
docs: Persists the underlying RDD with the specified storage level.