docs: def convert_to_string(self, block):
          """
          Takes a list of SeqRecordExpanded objects corresponding to a gene_code
          and produces the gene_block as string.
  
          :param block:
          :return: str.
          """
          if self.aminoacids:
              molecule_type = "protein"
          else:
              molecule_type = "dna"
  
          out = None
          for seq_record in block:
              if not out:
                  out = '&[{0}]\n'.format(molecule_type, seq_record.gene_code)
              taxon_id = '{0}_{1}_{2}'.format(seq_record.voucher_code,
                                              seq_record.taxonomy['genus'],
                                              seq_record.taxonomy['species'],
                                              )
              sequence = get_seq(seq_record, self.codon_positions, self.aminoacids,
                                 self.degenerate)
              seq = sequence.seq
              if sequence.warning:
                  self.warnings.append(sequence.warning)
  
              out += '{0}{1}\n'.format(taxon_id.ljust(55), seq)
          return out