def _truncate_seq_pair(tokens_a, tokens_b, max_length):
    """Truncates a sequence pair in place to the maximum length.

     This will always truncate the longer sequence one token at a time.
     This makes more sense than truncating an equal percent
     of tokens from each, since if one sequence is very short then each token
     that's truncated likely contains more information than a longer sequence.
    """
    while True:
        total_length = len(tokens_a) + len(tokens_b)
        if total_length <= max_length:
            break
        if len(tokens_a) > len(tokens_b):
            tokens_a.pop()
        else:
            tokens_b.pop()
