def create_library(name, record, chrom, begin, end=None, flank_size=20):
    """ Create a library line 

    record should be a pysam FastaFile

    """
    if not end:
        end = begin + 1

    left_marker = record.fetch(reference=chrom, start=begin-flank_size, end=begin)
    right_marker = record.fetch(reference=chrom, start=end, end=end+flank_size)
    expected_allele = record.fetch(reference=chrom, start=begin, end=end)

    return f'{name}\t{left_marker}\t{right_marker}\t{expected_allele} 1 1'