code: def pprint_sequence(sequence, annotations=None, block_length=10,
                      blocks_per_line=6, format=PlaintextFormat):
      annotations = annotations or []
      partitioning = partition_range(len(sequence), annotations)
      margin = int(math.floor(math.log(max(len(sequence), 1), 10))
                   + 1) + len(format.margin[0])
      result = (format.margin[0] + '1').rjust(margin) + format.margin[1] + ' '
      for p in range(0, len(sequence), block_length):
          block = [(max(start, p), min(stop, p + block_length), levels)
                   for start, stop, levels in partitioning
                   if start < p + block_length and stop > p]
          result += ' '
          for start, stop, levels in block:
              delimiters = [(left, right) for level, (left, right)
                            in enumerate(format.annotations) if level in levels]
              result += (''.join(left for left, right in reversed(delimiters)) +
                         str(sequence[start:stop]) +
                         ''.join(right for left, right in delimiters))
          if (not (p + block_length) % (block_length * blocks_per_line) and
              p + block_length < len(sequence)):
              result += ('\n' + (format.margin[0] +
                                 str(p + block_length + 1)).rjust(margin) +
                         format.margin[1] + ' ')
      return result