class_docstr: 使用 :class:`~fastNLP.modules.torch.encoder.LSTMSeq2SeqEncoder` 和 :class:`~fastNLP.modules.torch.decoder.LSTMSeq2SeqDecoder` 的
  :class:`Seq2SeqModel`，通过 :meth:`build_model` 方法初始化。
code: def __init__(self, encoder, decoder):
      super().__init__(encoder, decoder)
  
imports: import torch
  from torch import nn
  import torch.nn.functional
  from fastNLP import seq_len_to_mask
  from ...embeddings.torch.utils import get_embeddings
  from ...embeddings.torch.utils import get_sinusoid_encoding_table
  from ...modules.torch.decoder.seq2seq_decoder import Seq2SeqDecoder, TransformerSeq2SeqDecoder, LSTMSeq2SeqDecoder
  from ...modules.torch.encoder.seq2seq_encoder import Seq2SeqEncoder, TransformerSeq2SeqEncoder, LSTMSeq2SeqEncoder
label_desc: Use image node_id 1 to create a new LSTMSeq2SeqModel object from inherited base classes: Seq2SeqModel with example: obj = LSTMSeq2SeqModel(encoder, decoder)