def transcribe(records, transcribe):
    """
    Perform transcription or back-transcription.
    transcribe must be one of the following:
        dna2rna
        rna2dna
    """
    logging.info('Applying _transcribe generator: '
                 'operation to perform is ' + transcribe + '.')
    for record in records:
        sequence = str(record.seq)
        description = record.description
        name = record.id
        if transcribe == 'dna2rna':
            dna = Seq(sequence, IUPAC.ambiguous_dna)
            rna = dna.transcribe()
            yield SeqRecord(rna, id=name, description=description)
        elif transcribe == 'rna2dna':
            rna = Seq(sequence, IUPAC.ambiguous_rna)
            dna = rna.back_transcribe()
            yield SeqRecord(dna, id=name, description=description)