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# BERT

[BERT](https://huggingface.co/papers/1810.04805) 是一个在无标签的文本数据上预训练的双向 transformer，用于预测句子中被掩码的（masked） token，以及预测一个句子是否跟随在另一个句子之后。其主要思想是，在预训练过程中，通过随机掩码一些 token，让模型利用左右上下文的信息预测它们，从而获得更全面深入的理解。此外，BERT 具有很强的通用性，其学习到的语言表示可以通过额外的层或头进行微调，从而适配其他下游 NLP 任务。

你可以在 [BERT](https://huggingface.co/collections/google/bert-release-64ff5e7a4be99045d1896dbc) 集合下找到 BERT 的所有原始 checkpoint。

> [!TIP]
> 点击右侧边栏中的 BERT 模型，以查看将 BERT 应用于不同语言任务的更多示例。

下面的示例演示了如何使用 [`Pipeline`], [`AutoModel`] 和命令行预测 `[MASK]` token。

<hfoptions id="usage">
<hfoption id="Pipeline">

```py
import torch
from transformers import pipeline

pipeline = pipeline(
    task="fill-mask",
    model="google-bert/bert-base-uncased",
    dtype=torch.float16,
    device=0
)
pipeline("Plants create [MASK] through a process known as photosynthesis.")
```

</hfoption>
<hfoption id="AutoModel">

```py
import torch
from transformers import AutoModelForMaskedLM, AutoTokenizer

tokenizer = AutoTokenizer.from_pretrained(
    "google-bert/bert-base-uncased",
)
model = AutoModelForMaskedLM.from_pretrained(
    "google-bert/bert-base-uncased",
    dtype=torch.float16,
    device_map="auto",
    attn_implementation="sdpa"
)
inputs = tokenizer("Plants create [MASK] through a process known as photosynthesis.", return_tensors="pt").to("cuda")

with torch.no_grad():
    outputs = model(**inputs)
    predictions = outputs.logits

masked_index = torch.where(inputs['input_ids'] == tokenizer.mask_token_id)[1]
predicted_token_id = predictions[0, masked_index].argmax(dim=-1)
predicted_token = tokenizer.decode(predicted_token_id)

print(f"The predicted token is: {predicted_token}")
```

</hfoption>
<hfoption id="transformers">

```bash
echo -e "Plants create [MASK] through a process known as photosynthesis." | transformers run --task fill-mask --model google-bert/bert-base-uncased --device 0
```

</hfoption>
</hfoptions>

## 注意

- 输入内容应在右侧进行填充，因为 BERT 使用绝对位置嵌入。
## BertConfig

[[autodoc]] BertConfig
    - all

## BertTokenizer

[[autodoc]] BertTokenizer
    - get_special_tokens_mask
    - save_vocabulary

## BertTokenizerLegacy

[[autodoc]] BertTokenizerLegacy

## BertTokenizerFast

[[autodoc]] BertTokenizerFast

## BertModel

[[autodoc]] BertModel
    - forward

## BertForPreTraining

[[autodoc]] BertForPreTraining
    - forward

## BertLMHeadModel

[[autodoc]] BertLMHeadModel
    - forward

## BertForMaskedLM

[[autodoc]] BertForMaskedLM
    - forward

## BertForNextSentencePrediction

[[autodoc]] BertForNextSentencePrediction
    - forward

## BertForSequenceClassification

[[autodoc]] BertForSequenceClassification
    - forward

## BertForMultipleChoice

[[autodoc]] BertForMultipleChoice
    - forward

## BertForTokenClassification

[[autodoc]] BertForTokenClassification
    - forward

## BertForQuestionAnswering

[[autodoc]] BertForQuestionAnswering
    - forward

## Bert specific outputs

[[autodoc]] models.bert.modeling_bert.BertForPreTrainingOutput
