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from typing import Any, Dict, Optional, Tuple, Union
import torch
from torch import nn
from torch.utils.data import DistributedSampler, RandomSampler
from transformers import PreTrainedModel, Trainer, logging
from transformers.configuration_fsmt import FSMTConfig
from transformers.file_utils import is_torch_tpu_available
from transformers.optimization import (
Adafactor,
AdamW,
get_constant_schedule,
get_constant_schedule_with_warmup,
get_cosine_schedule_with_warmup,
get_cosine_with_hard_restarts_schedule_with_warmup,
get_linear_schedule_with_warmup,
get_polynomial_decay_schedule_with_warmup,
)
from transformers.trainer_pt_utils import get_tpu_sampler
logger = logging.get_logger(__name__)
arg_to_scheduler = {
"linear": get_linear_schedule_with_warmup,
"cosine": get_cosine_schedule_with_warmup,
"cosine_w_restarts": get_cosine_with_hard_restarts_schedule_with_warmup,
"polynomial": get_polynomial_decay_schedule_with_warmup,
"constant": get_constant_schedule,
"constant_w_warmup": get_constant_schedule_with_warmup,
}
class Seq2SeqTrainer(Trainer):
def __init__(self, config=None, data_args=None, *args, **kwargs):
super().__init__(*args, **kwargs)
if config is None:
assert isinstance(
self.model, PreTrainedModel
), f"If no `config` is passed the model to be trained has to be of type `PreTrainedModel`, but is {self.model.__class__}"
self.config = self._actual_model(self.model).config
else:
self.config = config
self.data_args = data_args
self.vocab_size = self.config.tgt_vocab_size if isinstance(self.config, FSMTConfig) else self.config.vocab_size
if self.args.label_smoothing != 0 or (self.data_args is not None and self.data_args.ignore_pad_token_for_loss):
assert (
self.config.pad_token_id is not None
), "Make sure that `config.pad_token_id` is correcly defined when ignoring `pad_token` for loss calculation or doing label smoothing."
if self.config.pad_token_id is None and self.config.eos_token_id is not None:
logger.warn(
f"The `config.pad_token_id` is `None`. Using `config.eos_token_id` = {self.config.eos_token_id} for padding.."
)
if self.args.label_smoothing == 0:
self.loss_fn = torch.nn.CrossEntropyLoss(ignore_index=self.config.pad_token_id)
else:
# dynamically import label_smoothed_nll_loss
from seq2seq_utils import label_smoothed_nll_loss
self.loss_fn = label_smoothed_nll_loss
def create_optimizer_and_scheduler(self, num_training_steps: int):
"""
Setup the optimizer and the learning rate scheduler.
We provide a reasonable default that works well. If you want to use something else, you can pass a tuple in the
Trainer's init through :obj:`optimizers`, or subclass and override this method in a subclass.
"""
if self.optimizer is None:
no_decay = ["bias", "LayerNorm.weight"]
optimizer_grouped_parameters = [
{
"params": [p for n, p in self.model.named_parameters() if not any(nd in n for nd in no_decay)],
"weight_decay": self.args.weight_decay,
},
{
"params": [p for n, p in self.model.named_parameters() if any(nd in n for nd in no_decay)],
"weight_decay": 0.0,
},
]
if self.args.adafactor:
self.optimizer = Adafactor(
optimizer_grouped_parameters,
lr=self.args.learning_rate,
scale_parameter=False,
relative_step=False,
)
else:
self.optimizer = AdamW(
optimizer_grouped_parameters, lr=self.args.learning_rate, eps=self.args.adam_epsilon
)
if self.lr_scheduler is None:
self.lr_scheduler = self._get_lr_scheduler(num_training_steps)
else: # ignoring --lr_scheduler
logger.warn("scheduler is passed to `Seq2SeqTrainer`, `--lr_scheduler` arg is ignored.")
def _get_lr_scheduler(self, num_training_steps):
schedule_func = arg_to_scheduler[self.args.lr_scheduler]
if self.args.lr_scheduler == "constant":
scheduler = schedule_func(self.optimizer)
elif self.args.lr_scheduler == "constant_w_warmup":
scheduler = schedule_func(self.optimizer, num_warmup_steps=self.args.warmup_steps)
else:
scheduler = schedule_func(
self.optimizer, num_warmup_steps=self.args.warmup_steps, num_training_steps=num_training_steps
)
return scheduler
def _get_train_sampler(self) -> Optional[torch.utils.data.sampler.Sampler]:
if isinstance(self.train_dataset, torch.utils.data.IterableDataset):
return None
elif is_torch_tpu_available():
return get_tpu_sampler(self.train_dataset)
else:
if self.args.sortish_sampler:
self.train_dataset.make_sortish_sampler(
self.args.per_device_train_batch_size, distributed=self.args.n_gpu > 1
)
return (
RandomSampler(self.train_dataset)
if self.args.local_rank == -1
else DistributedSampler(self.train_dataset)
)
def _compute_loss(self, model, inputs, labels):
if self.args.label_smoothing == 0:
if self.data_args is not None and self.data_args.ignore_pad_token_for_loss:
# force training to ignore pad token
logits = model(**inputs, use_cache=False)[0]
loss = self.loss_fn(logits.view(-1, logits.shape[-1]), labels.view(-1))
else:
# compute usual loss via models
loss, logits = model(**inputs, labels=labels, use_cache=False)[:2]
else:
# compute label smoothed loss
logits = model(**inputs, use_cache=False)[0]
lprobs = torch.nn.functional.log_softmax(logits, dim=-1)
loss, _ = self.loss_fn(lprobs, labels, self.args.label_smoothing, ignore_index=self.config.pad_token_id)
return loss, logits
def compute_loss(self, model, inputs):
labels = inputs.pop("labels")
loss, _ = self._compute_loss(model, inputs, labels)
return loss
def prediction_step(
self, model: nn.Module, inputs: Dict[str, Union[torch.Tensor, Any]], prediction_loss_only: bool
) -> Tuple[Optional[float], Optional[torch.Tensor], Optional[torch.Tensor]]:
"""
Perform an evaluation step on :obj:`model` using obj:`inputs`.
Subclass and override to inject custom behavior.
Args:
model (:obj:`nn.Module`):
The model to evaluate.
inputs (:obj:`Dict[str, Union[torch.Tensor, Any]]`):
The inputs and targets of the model.
The dictionary will be unpacked before being fed to the model. Most models expect the targets under the
argument :obj:`labels`. Check your model's documentation for all accepted arguments.
prediction_loss_only (:obj:`bool`):
Whether or not to return the loss only.
Return:
Tuple[Optional[float], Optional[torch.Tensor], Optional[torch.Tensor]]:
A tuple with the loss, logits and labels (each being optional).
"""
inputs = self._prepare_inputs(inputs)
gen_kwargs = {
"max_length": self.data_args.val_max_target_length
if self.data_args is not None
else self.config.max_length,
"num_beams": self.data_args.eval_beams if self.data_args is not None else self.config.num_beams,
}
if self.args.predict_with_generate and not self.args.prediction_loss_only:
generated_tokens = model.generate(
inputs["input_ids"],
attention_mask=inputs["attention_mask"],
**gen_kwargs,
)
# in case the batch is shorter than max length, the output should be padded
if generated_tokens.shape[-1] < gen_kwargs["max_length"]:
generated_tokens = self._pad_tensors_to_max_len(generated_tokens, gen_kwargs["max_length"])
labels = inputs.pop("labels")
with torch.no_grad():
# compute loss on predict data
loss, logits = self._compute_loss(model, inputs, labels)
loss = loss.mean().detach()
if self.args.prediction_loss_only:
return (loss, None, None)
logits = generated_tokens if self.args.predict_with_generate else logits
if labels.shape[-1] < gen_kwargs["max_length"]:
labels = self._pad_tensors_to_max_len(labels, gen_kwargs["max_length"])
return (loss, logits, labels)
def _pad_tensors_to_max_len(self, tensor, max_length):
# If PAD token is not defined at least EOS token has to be defined
pad_token_id = self.config.pad_token_id if self.config.pad_token_id is not None else self.config.eos_token_id
if pad_token_id is None:
raise ValueError(
f"Make sure that either `config.pad_token_id` or `config.eos_token_id` is defined if tensor has to be padded to `max_length`={max_length}"
)
padded_tensor = pad_token_id * torch.ones(
(tensor.shape[0], max_length), dtype=tensor.dtype, device=tensor.device
)
padded_tensor[:, : tensor.shape[-1]] = tensor
return padded_tensor
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