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# Copyright 2018 The HuggingFace Inc. team.
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# http://www.apache.org/licenses/LICENSE-2.0
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""" Classes to support Encoder-Decoder architectures """
import logging
from typing import Optional
from .configuration_encoder_decoder import EncoderDecoderConfig
from .configuration_utils import PretrainedConfig
from .modeling_utils import PreTrainedModel
logger = logging.getLogger(__name__)
[docs]class EncoderDecoderModel(PreTrainedModel):
r"""
:class:`~transformers.EncoderDecoder` is a generic model class that will be
instantiated as a transformer architecture with one of the base model
classes of the library as encoder and another one as
decoder when created with the `AutoModel.from_pretrained(pretrained_model_name_or_path)`
class method for the encoder and `AutoModelForCausalLM.from_pretrained(pretrained_model_name_or_path)` class method for the decoder.
"""
config_class = EncoderDecoderConfig
base_model_prefix = "encoder_decoder"
def __init__(
self,
config: Optional[PretrainedConfig] = None,
encoder: Optional[PreTrainedModel] = None,
decoder: Optional[PreTrainedModel] = None,
):
assert config is not None or (
encoder is not None and decoder is not None
), "Either a configuration or an Encoder and a decoder has to be provided"
if config is None:
config = EncoderDecoderConfig.from_encoder_decoder_configs(encoder.config, decoder.config)
else:
assert isinstance(config, self.config_class), "config: {} has to be of type {}".format(
config, self.config_class
)
# initialize with config
super().__init__(config)
if encoder is None:
from transformers import AutoModel
encoder = AutoModel.from_config(config.encoder)
if decoder is None:
from transformers import AutoModelForCausalLM
decoder = AutoModelForCausalLM.from_config(config.decoder)
self.encoder = encoder
self.decoder = decoder
assert (
self.encoder.get_output_embeddings() is None
), "The encoder {} should not have a LM Head. Please use a model without LM Head"
[docs] def tie_weights(self):
# for now no weights tying in encoder-decoder
pass
def get_encoder(self):
return self.encoder
def get_decoder(self):
return self.decoder
[docs] def get_output_embeddings(self):
return self.decoder.get_output_embeddings()
[docs] @classmethod
def from_encoder_decoder_pretrained(
cls,
encoder_pretrained_model_name_or_path: str = None,
decoder_pretrained_model_name_or_path: str = None,
*model_args,
**kwargs
) -> PreTrainedModel:
r""" Instantiates an encoder and a decoder from one or two base classes of the library from pre-trained model checkpoints.
The model is set in evaluation mode by default using `model.eval()` (Dropout modules are deactivated).
To train the model, you need to first set it back in training mode with `model.train()`.
Params:
encoder_pretrained_model_name_or_path (:obj: `str`, `optional`, defaults to `None`):
information necessary to initiate the encoder. Either:
- a string with the `shortcut name` of a pre-trained model to load from cache or download, e.g.: ``bert-base-uncased``.
- a string with the `identifier name` of a pre-trained model that was user-uploaded to our S3, e.g.: ``dbmdz/bert-base-german-cased``.
- a path to a `directory` containing model weights saved using :func:`~transformers.PreTrainedModel.save_pretrained`, e.g.: ``./my_model_directory/encoder``.
- a path or url to a `tensorflow index checkpoint file` (e.g. `./tf_model/model.ckpt.index`). In this case, ``from_tf`` should be set to True and a configuration object should be provided as ``config`` argument. This loading path is slower than converting the TensorFlow checkpoint in a PyTorch model using the provided conversion scripts and loading the PyTorch model afterwards.
decoder_pretrained_model_name_or_path (:obj: `str`, `optional`, defaults to `None`):
information necessary to initiate the decoder. Either:
- a string with the `shortcut name` of a pre-trained model to load from cache or download, e.g.: ``bert-base-uncased``.
- a string with the `identifier name` of a pre-trained model that was user-uploaded to our S3, e.g.: ``dbmdz/bert-base-german-cased``.
- a path to a `directory` containing model weights saved using :func:`~transformers.PreTrainedModel.save_pretrained`, e.g.: ``./my_model_directory/decoder``.
- a path or url to a `tensorflow index checkpoint file` (e.g. `./tf_model/model.ckpt.index`). In this case, ``from_tf`` should be set to True and a configuration object should be provided as ``config`` argument. This loading path is slower than converting the TensorFlow checkpoint in a PyTorch model using the provided conversion scripts and loading the PyTorch model afterwards.
model_args: (`optional`) Sequence of positional arguments:
All remaning positional arguments will be passed to the underlying model's ``__init__`` method
kwargs: (`optional`) Remaining dictionary of keyword arguments.
Can be used to update the configuration object (after it being loaded) and initiate the model. (e.g. ``output_attention=True``). Behave differently depending on whether a `config` is provided or automatically loaded:
Examples::
>>> from transformers import EncoderDecoderModel
>>> model = EncoderDecoderModel.from_encoder_decoder_pretrained('bert-base-uncased', 'bert-base-uncased') # initialize Bert2Bert
"""
kwargs_encoder = {
argument[len("encoder_") :]: value for argument, value in kwargs.items() if argument.startswith("encoder_")
}
kwargs_decoder = {
argument[len("decoder_") :]: value for argument, value in kwargs.items() if argument.startswith("decoder_")
}
# Load and initialize the encoder and decoder
# The distinction between encoder and decoder at the model level is made
# by the value of the flag `is_decoder` that we need to set correctly.
encoder = kwargs_encoder.pop("model", None)
if encoder is None:
assert (
encoder_pretrained_model_name_or_path is not None
), "If `model` is not defined as an argument, a `encoder_pretrained_model_name_or_path` has to be defined"
from .modeling_auto import AutoModel
encoder = AutoModel.from_pretrained(encoder_pretrained_model_name_or_path, *model_args, **kwargs_encoder)
encoder.config.is_decoder = False
decoder = kwargs_decoder.pop("model", None)
if decoder is None:
assert (
decoder_pretrained_model_name_or_path is not None
), "If `decoder_model` is not defined as an argument, a `decoder_pretrained_model_name_or_path` has to be defined"
from .modeling_auto import AutoModelForCausalLM
if "config" not in kwargs_decoder:
from transformers import AutoConfig
decoder_config = AutoConfig.from_pretrained(decoder_pretrained_model_name_or_path)
if decoder_config.is_decoder is False:
logger.info(
f"Initializing {decoder_pretrained_model_name_or_path} as a decoder model. Cross attention layers are added to {decoder_pretrained_model_name_or_path} and randomly initialized if {decoder_pretrained_model_name_or_path}'s architecture allows for cross attention layers."
)
decoder_config.is_decoder = True
kwargs_decoder["config"] = decoder_config
if kwargs_decoder["config"].is_decoder is False:
logger.warning(
f"Decoder model {decoder_pretrained_model_name_or_path} is not initialized as a decoder. In order to initialize {decoder_pretrained_model_name_or_path} as a decoder, make sure that the attribute `is_decoder` of `decoder_config` passed to `.from_encoder_decoder_pretrained(...)` is set to `True` or do not pass a `decoder_config` to `.from_encoder_decoder_pretrained(...)`"
)
decoder = AutoModelForCausalLM.from_pretrained(decoder_pretrained_model_name_or_path, **kwargs_decoder)
return cls(encoder=encoder, decoder=decoder)
[docs] def forward(
self,
input_ids=None,
inputs_embeds=None,
attention_mask=None,
head_mask=None,
encoder_outputs=None,
decoder_input_ids=None,
decoder_attention_mask=None,
decoder_head_mask=None,
decoder_inputs_embeds=None,
labels=None,
**kwargs,
):
"""
Args:
input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`):
Indices of input sequence tokens in the vocabulary for the encoder.
Indices can be obtained using :class:`transformers.PretrainedTokenizer`.
See :func:`transformers.PreTrainedTokenizer.encode` and
:func:`transformers.PreTrainedTokenizer.convert_tokens_to_ids` for details.
inputs_embeds (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length, hidden_size)`, `optional`, defaults to :obj:`None`):
Optionally, instead of passing :obj:`input_ids` you can choose to directly pass an embedded representation.
This is useful if you want more control over how to convert `input_ids` indices into associated vectors
than the model's internal embedding lookup matrix.
attention_mask (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`, defaults to :obj:`None`):
Mask to avoid performing attention on padding token indices for the encoder.
Mask values selected in ``[0, 1]``:
``1`` for tokens that are NOT MASKED, ``0`` for MASKED tokens.
head_mask: (:obj:`torch.FloatTensor` of shape :obj:`(num_heads,)` or :obj:`(num_layers, num_heads)`, `optional`, defaults to :obj:`None`):
Mask to nullify selected heads of the self-attention modules for the encoder.
Mask values selected in ``[0, 1]``:
``1`` indicates the head is **not masked**, ``0`` indicates the head is **masked**.
encoder_outputs (:obj:`tuple(tuple(torch.FloatTensor)`, `optional`, defaults to :obj:`None`):
Tuple consists of (`last_hidden_state`, `optional`: `hidden_states`, `optional`: `attentions`)
`last_hidden_state` of shape :obj:`(batch_size, sequence_length, hidden_size)`, `optional`, defaults to :obj:`None`) is a sequence of hidden-states at the output of the last layer of the encoder.
Used in the cross-attention of the decoder.
decoder_input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, target_sequence_length)`, `optional`, defaults to :obj:`None`):
Provide for sequence to sequence training to the decoder.
Indices can be obtained using :class:`transformers.PretrainedTokenizer`.
See :func:`transformers.PreTrainedTokenizer.encode` and
:func:`transformers.PreTrainedTokenizer.convert_tokens_to_ids` for details.
decoder_attention_mask (:obj:`torch.BoolTensor` of shape :obj:`(batch_size, tgt_seq_len)`, `optional`, defaults to :obj:`None`):
Default behavior: generate a tensor that ignores pad tokens in decoder_input_ids. Causal mask will also be used by default.
decoder_head_mask: (:obj:`torch.FloatTensor` of shape :obj:`(num_heads,)` or :obj:`(num_layers, num_heads)`, `optional`, defaults to :obj:`None`):
Mask to nullify selected heads of the self-attention modules for the decoder.
Mask values selected in ``[0, 1]``:
``1`` indicates the head is **not masked**, ``0`` indicates the head is **masked**.
decoder_inputs_embeds (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, target_sequence_length, hidden_size)`, `optional`, defaults to :obj:`None`):
Optionally, instead of passing :obj:`decoder_input_ids` you can choose to directly pass an embedded representation.
This is useful if you want more control over how to convert `decoder_input_ids` indices into associated vectors
than the model's internal embedding lookup matrix.
labels (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`, `optional`, defaults to :obj:`None`):
Labels for computing the masked language modeling loss for the decoder.
Indices should be in ``[-100, 0, ..., config.vocab_size]`` (see ``input_ids`` docstring)
Tokens with indices set to ``-100`` are ignored (masked), the loss is only computed for the tokens with labels
in ``[0, ..., config.vocab_size]``
kwargs: (`optional`) Remaining dictionary of keyword arguments. Keyword arguments come in two flavors:
- Without a prefix which will be input as `**encoder_kwargs` for the encoder forward function.
- With a `decoder_` prefix which will be input as `**decoder_kwargs` for the decoder forward function.
Examples::
>>> from transformers import EncoderDecoderModel, BertTokenizer
>>> import torch
>>> tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
>>> model = EncoderDecoderModel.from_encoder_decoder_pretrained('bert-base-uncased', 'bert-base-uncased') # initialize Bert2Bert
>>> # forward
>>> input_ids = torch.tensor(tokenizer.encode("Hello, my dog is cute", add_special_tokens=True)).unsqueeze(0) # Batch size 1
>>> outputs = model(input_ids=input_ids, decoder_input_ids=input_ids)
>>> # training
>>> loss, outputs = model(input_ids=input_ids, decoder_input_ids=input_ids, labels=input_ids)[:2]
>>> # generation
>>> generated = model.generate(input_ids, decoder_start_token_id=model.config.decoder.pad_token_id)
"""
kwargs_encoder = {argument: value for argument, value in kwargs.items() if not argument.startswith("decoder_")}
kwargs_decoder = {
argument[len("decoder_") :]: value for argument, value in kwargs.items() if argument.startswith("decoder_")
}
if encoder_outputs is None:
encoder_outputs = self.encoder(
input_ids=input_ids,
attention_mask=attention_mask,
inputs_embeds=inputs_embeds,
head_mask=head_mask,
**kwargs_encoder,
)
hidden_states = encoder_outputs[0]
# Decode
decoder_outputs = self.decoder(
input_ids=decoder_input_ids,
inputs_embeds=decoder_inputs_embeds,
attention_mask=decoder_attention_mask,
encoder_hidden_states=hidden_states,
encoder_attention_mask=attention_mask,
head_mask=decoder_head_mask,
labels=labels,
**kwargs_decoder,
)
return decoder_outputs + encoder_outputs
def prepare_inputs_for_generation(self, input_ids, past, attention_mask, **kwargs):
assert past is not None, "past has to be defined for encoder_outputs"
# first step
if type(past) is tuple:
encoder_outputs, _ = past
else:
encoder_outputs = (past,)
decoder_inputs = self.decoder.prepare_inputs_for_generation(input_ids)
return {
"attention_mask": attention_mask,
"decoder_attention_mask": decoder_inputs["attention_mask"],
"decoder_input_ids": decoder_inputs["input_ids"],
"encoder_outputs": encoder_outputs,
}
def _reorder_cache(self, past, beam_idx):
# as a default encoder-decoder models do not re-order the past.
# TODO(PVP): might have to be updated, e.g. if GPT2 is to be used as a decoder
return past