code: def get_self_attention_bias(x):
    
  
    x_shape = common_layers.shape_list(x)
    self_attention_bias = common_attention.attention_bias_lower_triangle(
        x_shape[1])
    return self_attention_bias
docs: Creates masked self attention bias.
  
    Args:
      x: A tensor of shape [batch, length, depth]
  
    Returns:
      self_attention_bias: A tensor of shape [length, length, 1]