def stock2one(stock):
    """
    convert stockholm to single line format
    """
    lines = {}
    for line in stock:
        line = line.strip()
        if print_line(line) is True:
            yield line
            continue
        if line.startswith('//'):
            continue
        ID, seq = line.rsplit(' ', 1)
        if ID not in lines:
            lines[ID] = ''
        else:
            # remove preceding white space
            seq = seq.strip()
        lines[ID] += seq
    for ID, line in lines.items():
        yield '\t'.join([ID, line])
    yield '\n//'
convert stockholm to single line format