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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def truncate_seq_pair(tokens_a, tokens_b, max_num_tokens, rng):
 """Truncates a pair of sequences to a maximum sequence length."""

    while True:
        total_length = len(tokens_a) + len(tokens_b)
        if total_length <= max_num_tokens:
            break

        trunc_tokens = tokens_a if len(tokens_a) > len(tokens_b) else tokens_b
        assert len(trunc_tokens) >= 1

        # We want to sometimes truncate from the front and sometimes from the
        # back to add more randomness and avoid biases.
        if rng.random() < 0.5:
            del trunc_tokens[0]
        else:
            trunc_tokens.pop()