def _qseq_to_protein_sequence(fh, seq_num=1,
                              phred_offset=_default_phred_offset,
                              variant=_default_variant, **kwargs):
    return _get_nth_sequence(_qseq_to_generator(fh, filter=False,
                             phred_offset=phred_offset, variant=variant,
                             constructor=Protein, **kwargs),
                             seq_num)

def _fastq_to_protein_sequence(fh, variant=None, phred_offset=None, seq_num=1,
                               **kwargs):
    return _get_nth_sequence(
        _fastq_to_generator(fh, variant=variant, phred_offset=phred_offset,
                            constructor=Protein,
                            **kwargs),
        seq_num)

def _construct_seq(fh, constructor=DNA, seq_num=1):
    lines = []
    for i, (data_type, seq_id, l) in enumerate(_yield_record(fh), 1):
        if data_type == 'data' and seq_num == i:
            lines = l
    seq = _get_nth_sequence(_fasta_to_generator(fh, constructor=constructor),
                            seq_num=seq_num)
    seq.interval_metadata = _parse_record(lines, len(seq))
    return seq

def _genbank_to_protein(fh, seq_num=1, **kwargs):
    record = _get_nth_sequence(_parse_genbanks(fh), seq_num)
    return _construct(record, Protein, **kwargs)

def _genbank_to_rna(fh, seq_num=1, **kwargs):
    record = _get_nth_sequence(_parse_genbanks(fh), seq_num)
    return _construct(record, RNA, **kwargs)

def _qseq_to_biological_sequence(fh, seq_num=1,
                                 phred_offset=_default_phred_offset,
                                 variant=_default_variant):
    return _get_nth_sequence(_qseq_to_generator(fh, filter=False,
                             phred_offset=phred_offset, variant=variant,
                             constructor=Sequence), seq_num)

 def test_seq_num_just_right(self):
     value = _get_nth_sequence(self.gen, 3)
     self.assertEqual(value, "goldilocks: 3")

    def test_seq_num_too_big(self):
        with self.assertRaises(ValueError) as cm:
            _get_nth_sequence(self.gen, 6)

        self.assertIn("end of file", str(cm.exception))
        self.assertIn("6th", str(cm.exception))

    def test_seq_num_too_small(self):
        with self.assertRaises(ValueError) as cm:
            _get_nth_sequence(self.gen, 0)

        self.assertIn("between 1 and", str(cm.exception))
        self.assertIn("0", str(cm.exception))

def _fasta_to_protein(fh, qual=FileSentinel, seq_num=1, **kwargs):
    return _get_nth_sequence(
        _fasta_to_generator(fh, qual=qual,
                            constructor=Protein, **kwargs),
        seq_num)

def _fastq_to_biological_sequence(fh, variant=None, phred_offset=None,
                                  seq_num=1):
    return _get_nth_sequence(
        _fastq_to_generator(fh, variant=variant, phred_offset=phred_offset,
                            constructor=Sequence),
        seq_num)

def _fasta_to_biological_sequence(fh, qual=FileSentinel, seq_num=1):
    return _get_nth_sequence(
        _fasta_to_generator(fh, qual=qual, constructor=Sequence),
        seq_num)

def _embl_to_RNA(fh, seq_num=1, **kwargs):
    record = _get_nth_sequence(_parse_records(fh, _parse_single_embl), seq_num)
    return _construct(record, RNA, **kwargs)

def _sam_to_RNA(fh, seq_num=1, **kwargs):
    record = _get_nth_sequence(_parse_records(fh), seq_num)
    return _construct(record, RNA, **kwargs)