---
library_name: keras-hub
---
## Model Overview
BART encoder-decoder network.

This class implements a Transformer-based encoder-decoder model as
described in
["BART: Denoising Sequence-to-Sequence Pre-training for Natural Language Generation, Translation, and Comprehension"](https://arxiv.org/abs/1910.13461).

The default constructor gives a fully customizable, randomly initialized BART
model with any number of layers, heads, and embedding dimensions. To load
preset architectures and weights, use the `from_preset` constructor.

Disclaimer: Pre-trained models are provided on an "as is" basis, without
warranties or conditions of any kind. The underlying model is provided by a
third party and subject to a separate license, available
[here](https://github.com/facebookresearch/fairseq/).


__Arguments__


- __vocabulary_size__: int. The size of the token vocabulary.
- __num_layers__: int. The number of transformer encoder layers and
    transformer decoder layers.
- __num_heads__: int. The number of attention heads for each transformer.
    The hidden size must be divisible by the number of attention heads.
- __hidden_dim__: int. The size of the transformer encoding and pooler layers.
- __intermediate_dim__: int. The output dimension of the first Dense layer in
    a two-layer feedforward network for each transformer.
- __dropout__: float. Dropout probability for the Transformer encoder.
- __max_sequence_length__: int. The maximum sequence length that this encoder
    can consume. If None, `max_sequence_length` uses the value from
    sequence length. This determines the variable shape for positional
    embeddings.

## Example Usage
```python
import keras
import keras_hub
import numpy as np
```

Use `generate()` to do text generation, given an input context.
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("bart_base_en")
bart_lm.generate("The quick brown fox", max_length=30)

# Generate with batched inputs.
bart_lm.generate(["The quick brown fox", "The whale"], max_length=30)
```

Compile the `generate()` function with a custom sampler.
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("bart_base_en")
bart_lm.compile(sampler="greedy")
bart_lm.generate("The quick brown fox", max_length=30)
```

Use `generate()` with encoder inputs and an incomplete decoder input (prompt).
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("bart_base_en")
bart_lm.generate(
    {
        "encoder_text": "The quick brown fox",
        "decoder_text": "The fast"
    }
)
```

Use `generate()` without preprocessing.
```python
# Preprocessed inputs, with encoder inputs corresponding to
# "The quick brown fox", and the decoder inputs to "The fast". Use
# `"padding_mask"` to indicate values that should not be overridden.
prompt = {
    "encoder_token_ids": np.array([[0, 133, 2119, 6219, 23602, 2, 1, 1]]),
    "encoder_padding_mask": np.array(
        [[True, True, True, True, True, True, False, False]]
    ),
    "decoder_token_ids": np.array([[2, 0, 133, 1769, 2, 1, 1]]),
    "decoder_padding_mask": np.array([[True, True, True, True, False, False]])
}

bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset(
    "bart_base_en",
    preprocessor=None,
)
bart_lm.generate(prompt)
```

Call `fit()` on a single batch.
```python
features = {
    "encoder_text": ["The quick brown fox jumped.", "I forgot my homework."],
    "decoder_text": ["The fast hazel fox leapt.", "I forgot my assignment."]
}
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("bart_base_en")
bart_lm.fit(x=features, batch_size=2)
```

Call `fit()` without preprocessing.
```python
x = {
    "encoder_token_ids": np.array([[0, 133, 2119, 2, 1]] * 2),
    "encoder_padding_mask": np.array([[1, 1, 1, 1, 0]] * 2),
    "decoder_token_ids": np.array([[2, 0, 133, 1769, 2]] * 2),
    "decoder_padding_mask": np.array([[1, 1, 1, 1, 1]] * 2),
}
y = np.array([[0, 133, 1769, 2, 1]] * 2)
sw = np.array([[1, 1, 1, 1, 0]] * 2)

bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset(
    "bart_base_en",
    preprocessor=None,
)
bart_lm.fit(x=x, y=y, sample_weight=sw, batch_size=2)
```

## Example Usage with Hugging Face URI

```python
import keras
import keras_hub
import numpy as np
```

Use `generate()` to do text generation, given an input context.
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("hf://keras/bart_base_en")
bart_lm.generate("The quick brown fox", max_length=30)

# Generate with batched inputs.
bart_lm.generate(["The quick brown fox", "The whale"], max_length=30)
```

Compile the `generate()` function with a custom sampler.
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("hf://keras/bart_base_en")
bart_lm.compile(sampler="greedy")
bart_lm.generate("The quick brown fox", max_length=30)
```

Use `generate()` with encoder inputs and an incomplete decoder input (prompt).
```python
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("hf://keras/bart_base_en")
bart_lm.generate(
    {
        "encoder_text": "The quick brown fox",
        "decoder_text": "The fast"
    }
)
```

Use `generate()` without preprocessing.
```python
# Preprocessed inputs, with encoder inputs corresponding to
# "The quick brown fox", and the decoder inputs to "The fast". Use
# `"padding_mask"` to indicate values that should not be overridden.
prompt = {
    "encoder_token_ids": np.array([[0, 133, 2119, 6219, 23602, 2, 1, 1]]),
    "encoder_padding_mask": np.array(
        [[True, True, True, True, True, True, False, False]]
    ),
    "decoder_token_ids": np.array([[2, 0, 133, 1769, 2, 1, 1]]),
    "decoder_padding_mask": np.array([[True, True, True, True, False, False]])
}

bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset(
    "hf://keras/bart_base_en",
    preprocessor=None,
)
bart_lm.generate(prompt)
```

Call `fit()` on a single batch.
```python
features = {
    "encoder_text": ["The quick brown fox jumped.", "I forgot my homework."],
    "decoder_text": ["The fast hazel fox leapt.", "I forgot my assignment."]
}
bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset("hf://keras/bart_base_en")
bart_lm.fit(x=features, batch_size=2)
```

Call `fit()` without preprocessing.
```python
x = {
    "encoder_token_ids": np.array([[0, 133, 2119, 2, 1]] * 2),
    "encoder_padding_mask": np.array([[1, 1, 1, 1, 0]] * 2),
    "decoder_token_ids": np.array([[2, 0, 133, 1769, 2]] * 2),
    "decoder_padding_mask": np.array([[1, 1, 1, 1, 1]] * 2),
}
y = np.array([[0, 133, 1769, 2, 1]] * 2)
sw = np.array([[1, 1, 1, 1, 0]] * 2)

bart_lm = keras_hub.models.BartSeq2SeqLM.from_preset(
    "hf://keras/bart_base_en",
    preprocessor=None,
)
bart_lm.fit(x=x, y=y, sample_weight=sw, batch_size=2)
```