def print_single(line, rev):
    """
    print single reads to stderr
    """
    if rev is True:
        seq = rc(['', line[9]])[1]
        qual = line[10][::-1]
    else:
        seq = line[9]
        qual = line[10]
    fq = ['@%s' % line[0], seq, '+%s' % line[0], qual]
    print('\n'.join(fq), file = sys.stderr)
print single reads to stderr