code: def _print_lines(self, lines, start, breaks=(), frame=None):
          
          if frame:
              current_lineno = frame.f_lineno
              exc_lineno = self.tb_lineno.get(frame, -1)
          else:
              current_lineno = exc_lineno = -1
          for lineno, line in enumerate(lines, start):
              s = str(lineno).rjust(3)
              if len(s) < 4:
                  s += ' '
              if lineno in breaks:
                  s += 'B'
              else:
                  s += ' '
              if lineno == current_lineno:
                  s += '->'
              elif lineno == exc_lineno:
                  s += '>>'
              self.message(s + '\t' + line.rstrip())
docs: Print a range of lines.