Source code for fairseq.modules.transformer_sentence_encoder

# Copyright (c) Facebook, Inc. and its affiliates.
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

from typing import Optional, Tuple

import torch
import torch.nn as nn
from fairseq.modules import (
from fairseq.modules.quant_noise import quant_noise as apply_quant_noise_

def init_bert_params(module):
    Initialize the weights specific to the BERT Model.
    This overrides the default initializations depending on the specified arguments.
        1. If normal_init_linear_weights is set then weights of linear
           layer will be initialized using the normal distribution and
           bais will be set to the specified value.
        2. If normal_init_embed_weights is set then weights of embedding
           layer will be initialized using the normal distribution.
        3. If normal_init_proj_weights is set then weights of
           in_project_weight for MultiHeadAttention initialized using
           the normal distribution (to be validated).

    if isinstance(module, nn.Linear):, std=0.02)
        if module.bias is not None:
    if isinstance(module, nn.Embedding):, std=0.02)
        if module.padding_idx is not None:
    if isinstance(module, MultiheadAttention):, std=0.02), std=0.02), std=0.02)

[docs]class TransformerSentenceEncoder(nn.Module): """ Implementation for a Bi-directional Transformer based Sentence Encoder used in BERT/XLM style pre-trained models. This first computes the token embedding using the token embedding matrix, position embeddings (if specified) and segment embeddings (if specified). After applying the specified number of TransformerEncoderLayers, it outputs all the internal states of the encoder as well as the final representation associated with the first token (usually CLS token). Input: - tokens: B x T matrix representing sentences - segment_labels: B x T matrix representing segment label for tokens Output: - a tuple of the following: - a list of internal model states used to compute the predictions where each tensor has shape T x B x C - sentence representation associated with first input token in format B x C. """ def __init__( self, padding_idx: int, vocab_size: int, num_encoder_layers: int = 6, embedding_dim: int = 768, ffn_embedding_dim: int = 3072, num_attention_heads: int = 8, dropout: float = 0.1, attention_dropout: float = 0.1, activation_dropout: float = 0.1, layerdrop: float = 0.0, max_seq_len: int = 256, num_segments: int = 2, use_position_embeddings: bool = True, offset_positions_by_padding: bool = True, encoder_normalize_before: bool = False, apply_bert_init: bool = False, activation_fn: str = "relu", learned_pos_embedding: bool = True, embed_scale: float = None, freeze_embeddings: bool = False, n_trans_layers_to_freeze: int = 0, export: bool = False, traceable: bool = False, q_noise: float = 0.0, qn_block_size: int = 8, ) -> None: super().__init__() self.padding_idx = padding_idx self.vocab_size = vocab_size self.dropout_module = FairseqDropout( dropout, module_name=self.__class__.__name__ ) self.layerdrop = layerdrop self.max_seq_len = max_seq_len self.embedding_dim = embedding_dim self.num_segments = num_segments self.use_position_embeddings = use_position_embeddings self.apply_bert_init = apply_bert_init self.learned_pos_embedding = learned_pos_embedding self.traceable = traceable self.tpu = False # whether we're on TPU self.embed_tokens = self.build_embedding( self.vocab_size, self.embedding_dim, self.padding_idx ) self.embed_scale = embed_scale if q_noise > 0: self.quant_noise = apply_quant_noise_( nn.Linear(self.embedding_dim, self.embedding_dim, bias=False), q_noise, qn_block_size, ) else: self.quant_noise = None self.segment_embeddings = ( nn.Embedding(self.num_segments, self.embedding_dim, padding_idx=None) if self.num_segments > 0 else None ) self.embed_positions = ( PositionalEmbedding( self.max_seq_len, self.embedding_dim, padding_idx=(self.padding_idx if offset_positions_by_padding else None), learned=self.learned_pos_embedding, ) if self.use_position_embeddings else None ) if self.layerdrop > 0.0: self.layers = LayerDropModuleList(p=self.layerdrop) else: self.layers = nn.ModuleList([]) self.layers.extend( [ self.build_transformer_sentence_encoder_layer( embedding_dim=self.embedding_dim, ffn_embedding_dim=ffn_embedding_dim, num_attention_heads=num_attention_heads, dropout=self.dropout_module.p, attention_dropout=attention_dropout, activation_dropout=activation_dropout, activation_fn=activation_fn, export=export, q_noise=q_noise, qn_block_size=qn_block_size, ) for _ in range(num_encoder_layers) ] ) if encoder_normalize_before: self.emb_layer_norm = LayerNorm(self.embedding_dim, export=export) else: self.emb_layer_norm = None # Apply initialization of model params after building the model if self.apply_bert_init: self.apply(init_bert_params) def freeze_module_params(m): if m is not None: for p in m.parameters(): p.requires_grad = False if freeze_embeddings: freeze_module_params(self.embed_tokens) freeze_module_params(self.segment_embeddings) freeze_module_params(self.embed_positions) freeze_module_params(self.emb_layer_norm) for layer in range(n_trans_layers_to_freeze): freeze_module_params(self.layers[layer])
[docs] def build_embedding(self, vocab_size, embedding_dim, padding_idx): return nn.Embedding(vocab_size, embedding_dim, padding_idx)
[docs] def build_transformer_sentence_encoder_layer( self, embedding_dim, ffn_embedding_dim, num_attention_heads, dropout, attention_dropout, activation_dropout, activation_fn, export, q_noise, qn_block_size, ): return TransformerSentenceEncoderLayer( embedding_dim=embedding_dim, ffn_embedding_dim=ffn_embedding_dim, num_attention_heads=num_attention_heads, dropout=dropout, attention_dropout=attention_dropout, activation_dropout=activation_dropout, activation_fn=activation_fn, export=export, q_noise=q_noise, qn_block_size=qn_block_size, )
[docs] def prepare_for_tpu_(self, **kwargs): self.tpu = True
[docs] def forward( self, tokens: torch.Tensor, segment_labels: torch.Tensor = None, last_state_only: bool = False, positions: Optional[torch.Tensor] = None, token_embeddings: Optional[torch.Tensor] = None, ) -> Tuple[torch.Tensor, torch.Tensor]: # compute padding mask. This is needed for multi-head attention padding_mask = tokens.eq(self.padding_idx) if not self.traceable and not self.tpu and not padding_mask.any(): padding_mask = None if token_embeddings is not None: x = token_embeddings else: x = self.embed_tokens(tokens) if self.embed_scale is not None: x = x * self.embed_scale if self.embed_positions is not None: x = x + self.embed_positions(tokens, positions=positions) if self.segment_embeddings is not None and segment_labels is not None: x = x + self.segment_embeddings(segment_labels) if self.quant_noise is not None: x = self.quant_noise(x) if self.emb_layer_norm is not None: x = self.emb_layer_norm(x) x = self.dropout_module(x) # account for padding while computing the representation if padding_mask is not None: x = x * (1 - padding_mask.unsqueeze(-1).type_as(x)) # B x T x C -> T x B x C x = x.transpose(0, 1) inner_states = [] if not last_state_only: inner_states.append(x) for layer in self.layers: x, _ = layer(x, self_attn_padding_mask=padding_mask) if not last_state_only: inner_states.append(x) sentence_rep = x[0, :, :] if last_state_only: inner_states = [x] if self.traceable: return torch.stack(inner_states), sentence_rep else: return inner_states, sentence_rep