def _get_matched_host_line_numbers(lines, enc):
    '''
    Helper function which parses ssh-keygen -F function output and yield line
    number of known_hosts entries with encryption key type matching enc,
    one by one.
    '''
    enc = enc if enc else "rsa"
    for i, line in enumerate(lines):
        if i % 2 == 0:
            line_no = int(line.strip().split()[-1])
            line_enc = lines[i + 1].strip().split()[-2]
            if line_enc != enc:
                continue
            yield line_no
Helper function which parses ssh-keygen -F function output and yield line
    number of known_hosts entries with encryption key type matching enc,
    one by one.