code: def _assign_folds(self):
      if self.fr is None:
          raise ValueError("No H2OFrame available for computing folds.")
      self.fold_assignments = self.fr.kfold_column(
          self.n_folds, self.seed
      )
      self.fr = None
  
file_path: h2o-3/h2o-py/h2o/cross_validation.py
imports: from h2o.utils.compatibility import *
label_desc: Use image node_id 4 for calling the H2OKFold obj's underlying member method code with example usage: obj._assign_folds() without return types