code: def extract_tokens(self, input_col='result', output_col='tokens'):
          
          return UASTsDataFrame(self._engine_dataframe.extractTokens(input_col, output_col),
                                self._session, self._implicits)
docs: Extracts the tokens from UAST nodes.
  
          >>> rows = uasts_df.query_uast('//*[@roleIdentifier]').extract_tokens().collect()
          >>> rows = uasts_df.query_uast('//*[@roleIdentifier]', output_col='foo').extract_tokens('foo', 'bar')
  
          :param input_col: column containing the list of nodes to extract tokens from
          :type input_col: str
          :param output_col: column to place the resultant tokens
          :type output_col: str
          :rtype: UASTsDataFrame