code: def _table_to_str(self):
          # type: () -> str
          
          _marker_line = self._marker_line()
          output = _marker_line + self._row_to_str(self.headers) + _marker_line
  
          for row in self._rows:
              output += self._row_to_str(row)
  
          output += _marker_line
  
          return output
docs: Return single formatted table string.
  
          :return: str