mbart.md

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*This model was released on 2020-01-22 and added to Hugging Face Transformers on 2020-11-16.*

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# mBART

[mBART](https://huggingface.co/papers/2001.08210) is a multilingual machine translation model that pretrains the entire translation model (encoder-decoder) unlike previous methods that only focused on parts of the model. The model is trained on a denoising objective which reconstructs the corrupted text. This allows mBART to handle the source language and the target text to translate to.

[mBART-50](https://huggingface.co/paper/2008.00401) is pretrained on an additional 25 languages.

You can find all the original mBART checkpoints under the [AI at Meta](https://huggingface.co/facebook?search_models=mbart) organization.

> [!TIP]
> Click on the mBART models in the right sidebar for more examples of applying mBART to different language tasks.

The example below demonstrates how to translate text with [`Pipeline`] or the [`AutoModel`] class.

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

```py
import torch
from transformers import pipeline

pipeline = pipeline(
    task="translation",
    model="facebook/mbart-large-50-many-to-many-mmt",
    device=0,
    dtype=torch.float16,
    src_lang="en_XX",
    tgt_lang="fr_XX",
)
print(pipeline("UN Chief Says There Is No Military Solution in Syria"))
```

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

```py
import torch
from transformers import AutoModelForSeq2SeqLM, AutoTokenizer

article_en = "UN Chief Says There Is No Military Solution in Syria"

model = AutoModelForSeq2SeqLM.from_pretrained("facebook/mbart-large-50-many-to-many-mmt", dtype=torch.bfloat16, attn_implementation="sdpa", device_map="auto")
tokenizer = AutoTokenizer.from_pretrained("facebook/mbart-large-50-many-to-many-mmt")

tokenizer.src_lang = "en_XX"
encoded_hi = tokenizer(article_en, return_tensors="pt").to(model.device)
generated_tokens = model.generate(**encoded_hi, forced_bos_token_id=tokenizer.lang_code_to_id["fr_XX"], cache_implementation="static")
print(tokenizer.batch_decode(generated_tokens, skip_special_tokens=True))
```

</hfoption>
</hfoptions>

## Notes

- You can check the full list of language codes via `tokenizer.lang_code_to_id.keys()`.
- mBART requires a special language id token in the source and target text during training. The source text format is `X [eos, src_lang_code]` where `X` is the source text. The target text format is `[tgt_lang_code] X [eos]`. The `bos` token is never used. The [`~PreTrainedTokenizerBase._call_`] encodes the source text format passed as the first argument or with the `text` keyword. The target text format is passed with the `text_label` keyword.
- Set the `decoder_start_token_id` to the target language id for mBART.

    ```py
    import torch
    from transformers import AutoModelForSeq2SeqLM, AutoTokenizer

    model = AutoModelForSeq2SeqLM.from_pretrained("facebook/mbart-large-en-ro", dtype=torch.bfloat16, attn_implementation="sdpa", device_map="auto")
    tokenizer = MBartTokenizer.from_pretrained("facebook/mbart-large-en-ro", src_lang="en_XX")

    article = "UN Chief Says There Is No Military Solution in Syria"
    inputs = tokenizer(article, return_tensors="pt")

    translated_tokens = model.generate(**inputs, decoder_start_token_id=tokenizer.lang_code_to_id["ro_RO"])
    tokenizer.batch_decode(translated_tokens, skip_special_tokens=True)[0]
    ```

- mBART-50 has a different text format. The language id token is used as the prefix for the source and target text. The text format is `[lang_code] X [eos]` where `lang_code` is the source language id for the source text and target language id for the target text. `X` is the source or target text respectively.
- Set the `eos_token_id` as the `decoder_start_token_id` for mBART-50. The target language id is used as the first generated token by passing `forced_bos_token_id` to [`~GenerationMixin.generate`].

    ```py
    import torch
    from transformers import AutoModelForSeq2SeqLM, AutoTokenizer

    model = AutoModelForSeq2SeqLM.from_pretrained("facebook/mbart-large-50-many-to-many-mmt", dtype=torch.bfloat16, attn_implementation="sdpa", device_map="auto")
    tokenizer = MBartTokenizer.from_pretrained("facebook/mbart-large-50-many-to-many-mmt")

    article_ar = "الأمين العام للأمم المتحدة يقول إنه لا يوجد حل عسكري في سوريا."
    tokenizer.src_lang = "ar_AR"

    encoded_ar = tokenizer(article_ar, return_tensors="pt")
    generated_tokens = model.generate(**encoded_ar, forced_bos_token_id=tokenizer.lang_code_to_id["en_XX"])
    tokenizer.batch_decode(generated_tokens, skip_special_tokens=True)
    ```

## MBartConfig

[[autodoc]] MBartConfig

## MBartTokenizer

[[autodoc]] MBartTokenizer
    - build_inputs_with_special_tokens

## MBartTokenizerFast

[[autodoc]] MBartTokenizerFast

## MBart50Tokenizer

[[autodoc]] MBart50Tokenizer

## MBart50TokenizerFast

[[autodoc]] MBart50TokenizerFast

## MBartModel

[[autodoc]] MBartModel

## MBartForConditionalGeneration

[[autodoc]] MBartForConditionalGeneration

## MBartForQuestionAnswering

[[autodoc]] MBartForQuestionAnswering

## MBartForSequenceClassification

[[autodoc]] MBartForSequenceClassification

## MBartForCausalLM

[[autodoc]] MBartForCausalLM
    - forward