code: def toString(self, format_='fasta-ss', structureSuffix=':structure'):
          
          if format_ == 'fasta-ss':
              return '>%s\n%s\n>%s%s\n%s\n' % (
                  self.id, self.sequence, self.id, structureSuffix,
                  self.structure)
          else:
              if six.PY3:
                  return super().toString(format_=format_)
              else:
                  return AARead.toString(self, format_=format_)
docs: Convert the read to a string in PDB format (sequence & structure). This
          consists of two FASTA records, one for the sequence then one for the
          structure.
  
          @param format_: Either 'fasta-ss' or 'fasta'. In the former case, the
              structure information is returned. Otherwise, plain FASTA is
              returned.
          @param structureSuffix: The C{str} suffix to append to the read id
              for the second FASTA record, containing the structure information.
          @raise ValueError: If C{format_} is not 'fasta'.
          @return: A C{str} representing the read sequence and structure in PDB
              FASTA format.