[BUG] 自定义模型，多个特征输入使用多个embed，模型fit报错，还需要重定义哪些方法来支持？

[Zikangli]

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Environment

• OS [e.g. Mac OS, Linux]: linux
• Python Version: python3.6.12
• kashgari: 2.0.2

Issue Description

我自定义了一个模型，模型需要输入多种特征（如词、词性、命名实体类别）。词特征用BertEmbedding获取，其他特征用BareEmbedding初始化，然后把它们拼接起来作为模型输入。模型定义都没问题，在相应tasks/labeling/init.py里面也加了，能调用，错误出现在fit的时候。

自定义模型的代码测试抽取如下（省略参数定义），是个序列标注任务：
def init(self,
embedding: ABCEmbedding = None,
posembedding: ABCEmbedding = None,
nerembedding: ABCEmbedding = None,
**kwargs
):
super(BiLSTM_TEST_Model, self).init()
self.embedding = embedding
self.posembedding = posembedding
self.nerembedding = nerembedding

def build_model_arc(self) -> None:
output_dim = self.label_processor.vocab_size

    config = self.hyper_parameters
    embed_model = self.embedding.embed_model
    embed_pos = self.posembedding.embed_model
    embed_ner = self.nerembedding.embed_model

    crf = KConditionalRandomField()
    bilstm = L.Bidirectional(L.LSTM(**config['layer_blstm']), name='layer_blstm')
    bilstm_dropout = L.Dropout(**config['layer_dropout'], name='layer_dropout')
    crf_dropout = L.Dropout(**config['layer_dropout'], name='crflayer_dropout')
    crf_dense = L.Dense(output_dim, **config['layer_time_distributed'])

    ## 三种特征的embed
    tensor_inputs = [tensor]
    model_inputs = [embed_model.inputs]
    if embed_pos != None:
        tensor_inputs.append(embed_pos.output)
        model_inputs.append(embed_pos.inputs)
    if embed_ner != None:
        tensor_inputs.append(embed_ner.output)
        model_inputs.append(embed_ner.inputs)
            
    tensor_con = L.concatenate(tensor_inputs, axis=2)    ## 把所有特征concate起来，作为输入
    bilstm_tensor = bilstm(tensor_con)
    bilstm_dropout_tensor = bilstm_dropout(bilstm_tensor)
    
    crf_dropout_tensor = crf_dropout(bilstm_dropout_tensor)
    crf_dense_tensor = crf_dense(crf_dropout_tensor)
    output = crf(crf_dense_tensor)

    self.tf_model = keras.Model(inputs=model_inputs, outputs=[output])
    self.crf_layer = crf

我在使用数据训练的时候，代码抽取如下：
def trainFunction(.....):
bert_embed = BertEmbedding('./Data/路径', sequence_length=maxlength)
pos_embed = BareEmbedding(embedding_size=32)
ner_embed = BareEmbedding(embedding_size=32)

    selfmodel = BiLSTM_TEST_Model(bert_embed, pos_embed, ner_embed, sequence_length=maxlength)
    history = selfmodel.fit(x_train=(train_x, train_pos_x, train_ner_x,), y_train=train_y, 
                            x_validate=(valid_x, valid_pos_x, valid_ner_x), y_validate=valid_y, batch_size=batchsize, epochs=12)

Reproduce

报错信息如下：
File "/venv/lib/python3.6/site-packages/kashgari/tasks/labeling/abc_model.py", line 177, in fit
fit_kwargs=fit_kwargs)
File "/venv/lib/python3.6/site-packages/kashgari/tasks/labeling/abc_model.py", line 208, in fit_generator
self.build_model_generator([g for g in [train_sample_gen, valid_sample_gen] if g])
File "/venv/lib/python3.6/site-packages/kashgari/tasks/labeling/abc_model.py", line 85, in build_model_generator
self.text_processor.build_vocab_generator(generators)
File "/venv/lib/python3.6/site-packages/kashgari/processors/sequence_processor.py", line 84, in build_vocab_generator
count = token2count.get(token, 0)
TypeError: unhashable type: 'list'

kashgari下build_vocab_generator()报错位置：
def build_vocab_generator(self,
generators: List[CorpusGenerator]) -> None:
if not self.vocab2idx:
vocab2idx = self._initial_vocab_dic

        token2count: Dict[str, int] = {}

        for gen in generators:
            for sentence, label in tqdm.tqdm(gen, desc="Preparing text vocab dict"):
                if self.build_vocab_from_labels:
                    target = label
                else:
                    target = sentence
                for token in target:      ## 我的输入是嵌套list，这里token是每一个list，就报错了。
                    count = token2count.get(token, 0)
                    token2count[token] = count + 1

DEBUG追踪看了下：我fit输入的x_train是三个，CorpusGenerator得到的generators的x也是嵌套的三个list，在build_vocab_generator的时候，就报错了。

我需要重定义build_vocab_generator吗？
除了这个地方，我的模型输入需要三个embedding model，这会导致我的self.vocab2idx/idx2vocab是不是也得定义三种，还有哪些地方需要我重新定义的吗？debug跟着跟着就晕了 T_T

求助！！

[Zikangli]

是不是模型的text_processor、label_processor也得相应的重新定义？

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