bert_classification.py

import logging
from typing import Optional, Tuple, Union

import torch
import torch.nn as nn
from torch.nn import BCEWithLogitsLoss, CrossEntropyLoss, MSELoss
from torch.nn.modules.utils import consume_prefix_in_state_dict_if_present
from transformers import BertPreTrainedModel
from transformers.modeling_outputs import SequenceClassifierOutput

from bert_layers_mosa import BertModel

logger = logging.getLogger(__name__)


class MosaicBertForSequenceClassification(BertPreTrainedModel):
    """Bert Model transformer with a sequence classification/regression head.

    This head is just a linear layer on top of the pooled output.
    """

    def __init__(self, config):
        super().__init__(config)
        self.num_labels = config.num_labels
        self.config = config
        self.bert = BertModel(config, add_pooling_layer=True)
        classifier_dropout = (
            config.classifier_dropout
            if config.classifier_dropout is not None
            else config.hidden_dropout_prob
        )
        self.dropout = nn.Dropout(classifier_dropout)
        self.classifier = nn.Linear(config.hidden_size, config.num_labels)

        # this resets the weights
        self.post_init()

    @classmethod
    def from_pretrained(
        cls, pretrained_checkpoint, state_dict=None, config=None, *inputs, **kwargs
    ):
        """Load from pre-trained."""
        # this gets a fresh init model
        model = cls(config, *inputs, **kwargs)

        # thus we need to load the state_dict
        state_dict = torch.load(pretrained_checkpoint)
        # remove `model` prefix to avoid error
        consume_prefix_in_state_dict_if_present(state_dict, prefix="model.")
        missing_keys, unexpected_keys = model.load_state_dict(state_dict, strict=False)

        if len(missing_keys) > 0:
            logger.warning(
                f"Found these missing keys in the checkpoint: {', '.join(missing_keys)}"
            )

            logger.warning(f"the number of which is equal to {len(missing_keys)}")

        if len(unexpected_keys) > 0:
            logger.warning(
                f"Found these unexpected keys in the checkpoint: {', '.join(unexpected_keys)}",
            )
            logger.warning(f"the number of which is equal to {len(unexpected_keys)}")

        return model

    def forward(
        self,
        input_ids: Optional[torch.Tensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        token_type_ids: Optional[torch.Tensor] = None,
        position_ids: Optional[torch.Tensor] = None,
        head_mask: Optional[torch.Tensor] = None,
        inputs_embeds: Optional[torch.Tensor] = None,
        labels: Optional[torch.Tensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple[torch.Tensor], SequenceClassifierOutput]:

        return_dict = (
            return_dict if return_dict is not None else self.config.use_return_dict
        )

        outputs = self.bert(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        pooled_output = outputs[1]

        pooled_output = self.dropout(pooled_output)
        logits = self.classifier(pooled_output)

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (
                    labels.dtype == torch.long or labels.dtype == torch.int
                ):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)
        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return SequenceClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=None,
            attentions=None,
        )