WeightedLayerPooling.py

import json
import os
from typing import Dict

import torch
from torch import Tensor, nn


class WeightedLayerPooling(nn.Module):
    """Token embeddings are weighted mean of their different hidden layer representations"""

    def __init__(
        self, word_embedding_dimension, num_hidden_layers: int = 12, layer_start: int = 4, layer_weights=None
    ):
        super(WeightedLayerPooling, self).__init__()
        self.config_keys = ["word_embedding_dimension", "layer_start", "num_hidden_layers"]
        self.word_embedding_dimension = word_embedding_dimension
        self.layer_start = layer_start
        self.num_hidden_layers = num_hidden_layers
        self.layer_weights = (
            layer_weights
            if layer_weights is not None
            else nn.Parameter(torch.tensor([1] * (num_hidden_layers + 1 - layer_start), dtype=torch.float))
        )

    def forward(self, features: Dict[str, Tensor]):
        ft_all_layers = features["all_layer_embeddings"]

        all_layer_embedding = torch.stack(ft_all_layers)
        all_layer_embedding = all_layer_embedding[self.layer_start :, :, :, :]  # Start from 4th layers output

        weight_factor = self.layer_weights.unsqueeze(-1).unsqueeze(-1).unsqueeze(-1).expand(all_layer_embedding.size())
        weighted_average = (weight_factor * all_layer_embedding).sum(dim=0) / self.layer_weights.sum()

        features.update({"token_embeddings": weighted_average})
        return features

    def get_word_embedding_dimension(self):
        return self.word_embedding_dimension

    def get_config_dict(self):
        return {key: self.__dict__[key] for key in self.config_keys}

    def save(self, output_path):
        with open(os.path.join(output_path, "config.json"), "w") as fOut:
            json.dump(self.get_config_dict(), fOut, indent=2)

        torch.save(self.state_dict(), os.path.join(output_path, "pytorch_model.bin"))

    @staticmethod
    def load(input_path):
        with open(os.path.join(input_path, "config.json")) as fIn:
            config = json.load(fIn)

        model = WeightedLayerPooling(**config)
        model.load_state_dict(
            torch.load(os.path.join(input_path, "pytorch_model.bin"), map_location=torch.device("cpu"))
        )
        return model