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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 _tls_mac_add(alg, c, write_seq_num):
 """ Compute the MAC using provided MAC alg instance over TLSCiphertext c using current write sequence number write_seq_num. Computed MAC is then appended to c.data and c.len is updated to reflect that change. It is the caller responsibility to increment the sequence number after the operation. The function has no return value. """

    write_seq_num = struct.pack("!Q", write_seq_num)
    h = alg.digest(write_seq_num + bytes(c))
    c.data += h
    c.len += alg.hash_len