docstr: :return: Composite or a single key for index
docstr_tok: [":","return",":","Composite","or","a","single","key","for","index"]
code: def key(self):
      """
      :return: Composite or a single key for index
      """
      raise NotImplementedError
  
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 2 for calling the BaseFeatureExporter obj's underlying member method code with example usage: obj.key() without return types