code: def variables(self) -> List[int]:
      return list(range(self._n_features))
  
imports: from operator import gt, le
  from typing import Any, List, Optional, Union
  import numpy
  import pandas
  from .errors import NoSplittableVariableException
  from .splitcondition import SplitCondition
label_desc: Use image node_id 14 for calling the CovariateMatrix obj's underlying member method code with example usage: obj.variables() and returns: list