code: def get_columns(self, index, columns=None, as_dict=False):
          
          i = sorted_index(self._index, index) if self._sort else self._index.index(index)
          return self.get_location(i, columns, as_dict)
docs: For a single index and list of column names return a DataFrame of the values in that index as either a dict
          or a DataFrame
  
          :param index: single index value
          :param columns: list of column names
          :param as_dict: if True then return the result as a dictionary
          :return: DataFrame or dictionary