code: def phred_13_to_18(self, new_path=None, in_place=True):
          
          # New file #
          if new_path is None: new_fastq = self.__class__(new_temp_path(suffix=self.extension))
          else:                new_fastq = self.__class__(new_path)
          # Do it #
          self.format = 'fastq-illumina'
          new_fastq.open('w')
          new_fastq.handle.writelines(seq.format('fastq-sanger') for seq in self)
          new_fastq.close()
          self.format = 'fastq-sanger'
          # Return #
          if in_place:
              os.remove(self.path)
              shutil.move(new_fastq, self.path)
              return self
          else: return new_fastq
docs: Illumina-1.3 format conversion to Illumina-1.8 format via BioPython.