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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 local_attention1d_masked_decoder(x, kv_dim, heads_dim, feedforward_dim, hparams):
 """Image Transformer decoder with local1D masked layers."""

  print(x)
  _, length_dim, model_dim = x.shape.dims
  for layer in range(hparams.num_decoder_layers):
    layer_name = "decoder_layer_%d" % layer
    with tf.variable_scope(layer_name):
      # Self attention layer
      length_per_split = mtf.tensor_dim_to_size_per_split(
          hparams.layout, hparams.mesh_shape, length_dim)
      x += layer_prepostprocess_dropout(
          mtf.layers.masked_local_attention_1d(
              mtf.layers.layer_norm(x, model_dim, name="layer_norm_att"),
              kv_dim,
              heads_dim,
              window_size=hparams.block_length,
              length_per_split=length_per_split,
              name="self_att"), hparams)
      # ffn layer
      x += layer_prepostprocess_dropout(
          mtf.layers.dense_relu_dense(
              mtf.layers.layer_norm(x, model_dim, name="layer_norm_ffn"),
              feedforward_dim,
              hparams.dropout,
              dropout_broadcast_dims=[length_dim]), hparams)

  output = mtf.layers.layer_norm(x, model_dim, name="final_layer_norm")
  return output