parameters: (index, i, column_names)
docstring: Return the name of an index level or a default name if `index.name` is
      None or is already a column name.
  
      Parameters
      ----------
      index : pandas.Index
      i : int
  
      Returns
      -------
      name : str
docstring_summary: Return the name of an index level or a default name if `index.name` is
      None or is already a column name.
docstring_tokens: Return the name of an index level or a default name if index . name is None or is already a column name .
function: def _index_level_name(index, i, column_names):
      """Return the name of an index level or a default name if `index.name` is
      None or is already a column name.
  
      Parameters
      ----------
      index : pandas.Index
      i : int
  
      Returns
      -------
      name : str
      """
      if index.name is not None and index.name not in column_names:
          return index.name
      else:
          return '__index_level_{:d}__'.format(i)
function_tokens: def _index_level_name ( index , i , column_names ) : if index . name is not None and index . name not in column_names : return index . name else : return '__index_level_{:d}__' . format ( i )