code: def init_write_line(self):
          
          format_list = self._format_list
          output_info = self.gen_output_fmt(format_list)
          self._output_fmt = "".join([sub[0] for sub in output_info])
          self._out_gen_fmt = [sub[1] for sub in output_info if sub[1] is not None]
          self._out_widths = [sub[2] for sub in output_info if sub[2] is not None]
          self._write_line_init = True
docs: init_write_line() initializes fields relevant to output generation