<p>有两种方法:由于您希望为类似于分类的下游任务微调模型,因此可以直接使用:</p>
<p><code>BertForSequenceClassification</code>类。在768的输出维度上执行逻辑回归层的微调</p>
<p>或者,您可以定义一个自定义模块,该模块基于预先训练的权重创建一个bert模型,并在其上添加层</p>
<pre><code>from transformers import BertModel
class CustomBERTModel(nn.Module):
def __init__(self):
super(CustomBERTModel, self).__init__()
self.bert = BertModel.from_pretrained("dbmdz/bert-base-italian-xxl-cased")
### New layers:
self.linear1 = nn.Linear(768, 256)
self.linear2 = nn.Linear(256, 3) ## 3 is the number of classes in this example
def forward(self, ids, mask):
sequence_output, pooled_output = self.bert(
ids,
attention_mask=mask)
# sequence_output has the following shape: (batch_size, sequence_length, 768)
linear1_output = self.linear1(sequence_output[:,0,:].view(-1,768)) ## extract the 1st token's embeddings
linear2_output = self.linear2(linear2_output)
return linear2_output
tokenizer = AutoTokenizer.from_pretrained("dbmdz/bert-base-italian-xxl-cased")
model = CustomBERTModel() # You can pass the parameters if required to have more flexible model
model.to(torch.device("cpu")) ## can be gpu
criterion = nn.CrossEntropyLoss() ## If required define your own criterion
optimizer = torch.optim.Adam(filter(lambda p: p.requires_grad, model.parameters()))
for epoch in epochs:
for batch in data_loader: ## If you have a DataLoader() object to get the data.
data = batch[0]
targets = batch[1] ## assuming that data loader returns a tuple of data and its targets
optimizer.zero_grad()
encoding = tokenizer.batch_encode_plus(data, return_tensors='pt', padding=True, truncation=True,max_length=50, add_special_tokens = True)
outputs = model(input_ids, attention_mask=attention_mask)
outputs = F.log_softmax(outputs, dim=1)
input_ids = encoding['input_ids']
attention_mask = encoding['attention_mask']
loss = criterion(outputs, targets)
loss.backward()
optimizer.step()
</code></pre>