def METHOD_NAME(self, peptides):
    with open(self.output_file, 'w') as out_f:
        for index, peptide in peptides.items():
            out_f.write(">%s\n" % index)
            out_f.write("%s\n" % peptide)
            print("ID: " + index + ", sequence: " + peptide)
    out_f.close()
    print("FASTA file written")