def _convert_past_list_to_tuple(past_key_values):
    """
    In Bart model, the type of past_key_values is tuple(tuple(torch.FloatTensor)) which is not
    TorchScript-compatible. To support this, we have to convert it during the export process.
    This function will convert past values from a list to tuple(tuple(torch.FloatTensor)) for
    the inner decoder.

    According to the definition of past_key_values, each inner tuple(torch.FloatTensor) has 4 tensors,
    so we convert every 4 elements in the list as a tuple(torch.FloatTensor).
    """
    count_of_each_inner_tuple = 4
    results = ()
    temp_result = ()
    count_n = len(past_key_values) // count_of_each_inner_tuple
    for idx in range(count_n):
        real_idx = idx * count_of_each_inner_tuple
        temp_result = tuple(past_key_values[real_idx : real_idx + count_of_each_inner_tuple])
        results += ((temp_result),)

    return results