{"record":{"id":"d6bf67a18256cfee","repo":"d2l-ai/d2l-zh","slug":"notimplementederror-d6bf67","errorCode":null,"errorMessage":"NotImplementedError","messagePattern":"NotImplementedError","errorType":"exception","errorClass":"NotImplementedError","httpStatus":null,"severity":"error","filePath":"d2l/paddle.py","lineNumber":949,"sourceCode":"    text = preprocess_nmt(read_data_nmt())\n    source, target = tokenize_nmt(text, num_examples)\n    src_vocab = d2l.Vocab(source, min_freq=2,\n                          reserved_tokens=['<pad>', '<bos>', '<eos>'])\n    tgt_vocab = d2l.Vocab(target, min_freq=2,\n                          reserved_tokens=['<pad>', '<bos>', '<eos>'])\n    src_array, src_valid_len = build_array_nmt(source, src_vocab, num_steps)\n    tgt_array, tgt_valid_len = build_array_nmt(target, tgt_vocab, num_steps)\n    data_arrays = (src_array, src_valid_len, tgt_array, tgt_valid_len)\n    data_iter = d2l.load_array(data_arrays, batch_size)\n    return data_iter, src_vocab, tgt_vocab\n\nclass Encoder(nn.Layer):\n    \"\"\"编码器-解码器架构的基本编码器接口\"\"\"\n    def __init__(self, **kwargs):\n        super(Encoder, self).__init__(**kwargs)\n\n    def forward(self, X, *args):\n        raise NotImplementedError\n\nclass Decoder(nn.Layer):\n    \"\"\"编码器-解码器架构的基本解码器接口\n\n    Defined in :numref:`sec_encoder-decoder`\"\"\"\n    def __init__(self, **kwargs):\n        super(Decoder, self).__init__(**kwargs)\n\n    def init_state(self, enc_outputs, *args):\n        raise NotImplementedError\n\n    def forward(self, X, state):\n        raise NotImplementedError\n\nclass EncoderDecoder(nn.Layer):\n    \"\"\"编码器-解码器架构的基类\n\n    Defined in :numref:`sec_encoder-decoder`\"\"\"","sourceCodeStart":931,"sourceCodeEnd":967,"githubUrl":"https://github.com/d2l-ai/d2l-zh/blob/e6b18ccea71451a55fcd861d7b96fddf2587b09a/d2l/paddle.py#L931-L967","documentation":"A NotImplementedError raised by d2l.paddle.Encoder.forward. Encoder is the abstract encoder interface of the encoder-decoder architecture in the PaddlePaddle edition; forward is intentionally unimplemented. A subclass that fails to override forward (or a direct instantiation) raises as soon as the layer is invoked.","triggerScenarios":"Calling d2l.Encoder()(X) directly; defining an encoder subclass with 'call' instead of 'forward' (TensorFlow spelling) so Paddle never dispatches to it; forgetting the override while implementing a custom architecture.","commonSituations":"Porting the TensorFlow d2l edition to Paddle and keeping the 'call' method name; exercises in sec_encoder-decoder where users build their own encoder; partial IDE-generated subclasses.","solutions":["Subclass and implement forward: class MyEncoder(d2l.Encoder): def forward(self, X, *args): ...","Rename 'call' to 'forward' when porting from the TensorFlow edition.","Use the provided d2l.Seq2SeqEncoder instead of the abstract base for standard seq2seq.","Verify the signature matches (self, X, *args) so EncoderDecoder.forward can invoke it."],"exampleFix":"# before\nenc = d2l.Encoder()\nenc(X)  # NotImplementedError\n# after\nclass MyEncoder(d2l.Encoder):\n    def forward(self, X, *args):\n        return paddle.identity(X)\nenc = MyEncoder()\nenc(X)","handlingStrategy":"type-guard","validationCode":null,"typeGuard":"def is_concrete_encoder(enc) -> bool:\n    return (isinstance(enc, d2l.Encoder)\n            and type(enc).forward is not d2l.Encoder.forward)","tryCatchPattern":"try:\n    enc(X)\nexcept NotImplementedError:\n    raise TypeError(f'{type(enc).__name__} must override Encoder.forward(X, *args)') from None","preventionTips":["In Paddle subclasses the method must be named forward (not call).","Smoke-test new encoders with a tiny forward pass before training.","Prefer d2l.Seq2SeqEncoder for standard seq2seq."],"tags":["d2l","paddle","encoder-decoder","abstract-class","notimplementederror"],"backgroundTag":null,"analyzedSha":"e6b18ccea71451a55fcd861d7b96fddf2587b09a","analyzedAt":"2026-08-14T20:05:26.414Z","schemaVersion":2},"datasetVersion":"2026-08-15T22:17:37.221Z"}