code: def _values(self):
      value_cols = set(self._raw_data.columns.values.tolist()) - set(
          self.key
      )
      if len(value_cols) > 1:
          raise ValueError("Only one feature column allowed")
      return list(value_cols)
  
imports: import datetime
  from abc import ABCMeta, abstractmethod
  import lore
  from lore.env import require
  from lore.util import convert_df_columns_to_json
  import pandas
  import inflection
label_desc: Use image node_id 9 for calling the BaseFeatureExporter obj's underlying member method code with example usage: obj._values() and returns: list