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modeling_bertabs.py
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# MIT License
# Copyright (c) 2019 Yang Liu and the HuggingFace team
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import copy
import math
import numpy as np
import torch
from torch import nn
from torch.nn.init import xavier_uniform_
from configuration_bertabs import BertAbsConfig
from transformers import BertConfig, BertModel, PreTrainedModel
MAX_SIZE = 5000
BERTABS_FINETUNED_MODEL_ARCHIVE_LIST = [
"remi/bertabs-finetuned-cnndm-extractive-abstractive-summarization",
]
class BertAbsPreTrainedModel(PreTrainedModel):
config_class = BertAbsConfig
load_tf_weights = False
base_model_prefix = "bert"
class BertAbs(BertAbsPreTrainedModel):
def __init__(self, args, checkpoint=None, bert_extractive_checkpoint=None):
super().__init__(args)
self.args = args
self.bert = Bert()
# If pre-trained weights are passed for Bert, load these.
load_bert_pretrained_extractive = True if bert_extractive_checkpoint else False
if load_bert_pretrained_extractive:
self.bert.model.load_state_dict(
dict([(n[11:], p) for n, p in bert_extractive_checkpoint.items() if n.startswith("bert.model")]),
strict=True,
)
self.vocab_size = self.bert.model.config.vocab_size
if args.max_pos > 512:
my_pos_embeddings = nn.Embedding(args.max_pos, self.bert.model.config.hidden_size)
my_pos_embeddings.weight.data[:512] = self.bert.model.embeddings.position_embeddings.weight.data
my_pos_embeddings.weight.data[512:] = self.bert.model.embeddings.position_embeddings.weight.data[-1][
None, :
].repeat(args.max_pos - 512, 1)
self.bert.model.embeddings.position_embeddings = my_pos_embeddings
tgt_embeddings = nn.Embedding(self.vocab_size, self.bert.model.config.hidden_size, padding_idx=0)
tgt_embeddings.weight = copy.deepcopy(self.bert.model.embeddings.word_embeddings.weight)
self.decoder = TransformerDecoder(
self.args.dec_layers,
self.args.dec_hidden_size,
heads=self.args.dec_heads,
d_ff=self.args.dec_ff_size,
dropout=self.args.dec_dropout,
embeddings=tgt_embeddings,
vocab_size=self.vocab_size,
)
gen_func = nn.LogSoftmax(dim=-1)
self.generator = nn.Sequential(nn.Linear(args.dec_hidden_size, args.vocab_size), gen_func)
self.generator[0].weight = self.decoder.embeddings.weight
load_from_checkpoints = False if checkpoint is None else True
if load_from_checkpoints:
self.load_state_dict(checkpoint)
def init_weights(self):
for module in self.decoder.modules():
if isinstance(module, (nn.Linear, nn.Embedding)):
module.weight.data.normal_(mean=0.0, std=0.02)
elif isinstance(module, nn.LayerNorm):
module.bias.data.zero_()
module.weight.data.fill_(1.0)
if isinstance(module, nn.Linear) and module.bias is not None:
module.bias.data.zero_()
for p in self.generator.parameters():
if p.dim() > 1:
xavier_uniform_(p)
else:
p.data.zero_()
def forward(
self,
encoder_input_ids,
decoder_input_ids,
token_type_ids,
encoder_attention_mask,
decoder_attention_mask,
):
encoder_output = self.bert(
input_ids=encoder_input_ids,
token_type_ids=token_type_ids,
attention_mask=encoder_attention_mask,
)
encoder_hidden_states = encoder_output[0]
dec_state = self.decoder.init_decoder_state(encoder_input_ids, encoder_hidden_states)
decoder_outputs, _ = self.decoder(decoder_input_ids[:, :-1], encoder_hidden_states, dec_state)
return decoder_outputs
class Bert(nn.Module):
"""This class is not really necessary and should probably disappear."""
def __init__(self):
super().__init__()
config = BertConfig.from_pretrained("bert-base-uncased")
self.model = BertModel(config)
def forward(self, input_ids, attention_mask=None, token_type_ids=None, **kwargs):
self.eval()
with torch.no_grad():
encoder_outputs, _ = self.model(
input_ids, token_type_ids=token_type_ids, attention_mask=attention_mask, **kwargs
)
return encoder_outputs
class TransformerDecoder(nn.Module):
"""
The Transformer decoder from "Attention is All You Need".
Args:
num_layers (int): number of encoder layers.
d_model (int): size of the model
heads (int): number of heads
d_ff (int): size of the inner FF layer
dropout (float): dropout parameters
embeddings (:obj:`onmt.modules.Embeddings`):
embeddings to use, should have positional encodings
attn_type (str): if using a separate copy attention
"""
def __init__(self, num_layers, d_model, heads, d_ff, dropout, embeddings, vocab_size):
super().__init__()
# Basic attributes.
self.decoder_type = "transformer"
self.num_layers = num_layers
self.embeddings = embeddings
self.pos_emb = PositionalEncoding(dropout, self.embeddings.embedding_dim)
# Build TransformerDecoder.
self.transformer_layers = nn.ModuleList(
[TransformerDecoderLayer(d_model, heads, d_ff, dropout) for _ in range(num_layers)]
)
self.layer_norm = nn.LayerNorm(d_model, eps=1e-6)
# forward(input_ids, attention_mask, encoder_hidden_states, encoder_attention_mask)
# def forward(self, input_ids, state, attention_mask=None, memory_lengths=None,
# step=None, cache=None, encoder_attention_mask=None, encoder_hidden_states=None, memory_masks=None):
def forward(
self,
input_ids,
encoder_hidden_states=None,
state=None,
attention_mask=None,
memory_lengths=None,
step=None,
cache=None,
encoder_attention_mask=None,
):
"""
See :obj:`onmt.modules.RNNDecoderBase.forward()`
memory_bank = encoder_hidden_states
"""
# Name conversion
tgt = input_ids
memory_bank = encoder_hidden_states
memory_mask = encoder_attention_mask
# src_words = state.src
src_words = state.src
src_batch, src_len = src_words.size()
padding_idx = self.embeddings.padding_idx
# Decoder padding mask
tgt_words = tgt
tgt_batch, tgt_len = tgt_words.size()
tgt_pad_mask = tgt_words.data.eq(padding_idx).unsqueeze(1).expand(tgt_batch, tgt_len, tgt_len)
# Encoder padding mask
if memory_mask is not None:
src_len = memory_mask.size(-1)
src_pad_mask = memory_mask.expand(src_batch, tgt_len, src_len)
else:
src_pad_mask = src_words.data.eq(padding_idx).unsqueeze(1).expand(src_batch, tgt_len, src_len)
# Pass through the embeddings
emb = self.embeddings(input_ids)
output = self.pos_emb(emb, step)
assert emb.dim() == 3 # len x batch x embedding_dim
if state.cache is None:
saved_inputs = []
for i in range(self.num_layers):
prev_layer_input = None
if state.cache is None:
if state.previous_input is not None:
prev_layer_input = state.previous_layer_inputs[i]
output, all_input = self.transformer_layers[i](
output,
memory_bank,
src_pad_mask,
tgt_pad_mask,
previous_input=prev_layer_input,
layer_cache=state.cache["layer_{}".format(i)] if state.cache is not None else None,
step=step,
)
if state.cache is None:
saved_inputs.append(all_input)
if state.cache is None:
saved_inputs = torch.stack(saved_inputs)
output = self.layer_norm(output)
if state.cache is None:
state = state.update_state(tgt, saved_inputs)
# Decoders in transformers return a tuple. Beam search will fail
# if we don't follow this convention.
return output, state # , state
def init_decoder_state(self, src, memory_bank, with_cache=False):
""" Init decoder state """
state = TransformerDecoderState(src)
if with_cache:
state._init_cache(memory_bank, self.num_layers)
return state
class PositionalEncoding(nn.Module):
def __init__(self, dropout, dim, max_len=5000):
pe = torch.zeros(max_len, dim)
position = torch.arange(0, max_len).unsqueeze(1)
div_term = torch.exp((torch.arange(0, dim, 2, dtype=torch.float) * -(math.log(10000.0) / dim)))
pe[:, 0::2] = torch.sin(position.float() * div_term)
pe[:, 1::2] = torch.cos(position.float() * div_term)
pe = pe.unsqueeze(0)
super().__init__()
self.register_buffer("pe", pe)
self.dropout = nn.Dropout(p=dropout)
self.dim = dim
def forward(self, emb, step=None):
emb = emb * math.sqrt(self.dim)
if step:
emb = emb + self.pe[:, step][:, None, :]
else:
emb = emb + self.pe[:, : emb.size(1)]
emb = self.dropout(emb)
return emb
def get_emb(self, emb):
return self.pe[:, : emb.size(1)]
class TransformerDecoderLayer(nn.Module):
"""
Args:
d_model (int): the dimension of keys/values/queries in
MultiHeadedAttention, also the input size of
the first-layer of the PositionwiseFeedForward.
heads (int): the number of heads for MultiHeadedAttention.
d_ff (int): the second-layer of the PositionwiseFeedForward.
dropout (float): dropout probability(0-1.0).
self_attn_type (string): type of self-attention scaled-dot, average
"""
def __init__(self, d_model, heads, d_ff, dropout):
super().__init__()
self.self_attn = MultiHeadedAttention(heads, d_model, dropout=dropout)
self.context_attn = MultiHeadedAttention(heads, d_model, dropout=dropout)
self.feed_forward = PositionwiseFeedForward(d_model, d_ff, dropout)
self.layer_norm_1 = nn.LayerNorm(d_model, eps=1e-6)
self.layer_norm_2 = nn.LayerNorm(d_model, eps=1e-6)
self.drop = nn.Dropout(dropout)
mask = self._get_attn_subsequent_mask(MAX_SIZE)
# Register self.mask as a saved_state in TransformerDecoderLayer, so
# it gets TransformerDecoderLayer's cuda behavior automatically.
self.register_buffer("mask", mask)
def forward(
self,
inputs,
memory_bank,
src_pad_mask,
tgt_pad_mask,
previous_input=None,
layer_cache=None,
step=None,
):
"""
Args:
inputs (`FloatTensor`): `[batch_size x 1 x model_dim]`
memory_bank (`FloatTensor`): `[batch_size x src_len x model_dim]`
src_pad_mask (`LongTensor`): `[batch_size x 1 x src_len]`
tgt_pad_mask (`LongTensor`): `[batch_size x 1 x 1]`
Returns:
(`FloatTensor`, `FloatTensor`, `FloatTensor`):
* output `[batch_size x 1 x model_dim]`
* attn `[batch_size x 1 x src_len]`
* all_input `[batch_size x current_step x model_dim]`
"""
dec_mask = torch.gt(tgt_pad_mask + self.mask[:, : tgt_pad_mask.size(1), : tgt_pad_mask.size(1)], 0)
input_norm = self.layer_norm_1(inputs)
all_input = input_norm
if previous_input is not None:
all_input = torch.cat((previous_input, input_norm), dim=1)
dec_mask = None
query = self.self_attn(
all_input,
all_input,
input_norm,
mask=dec_mask,
layer_cache=layer_cache,
type="self",
)
query = self.drop(query) + inputs
query_norm = self.layer_norm_2(query)
mid = self.context_attn(
memory_bank,
memory_bank,
query_norm,
mask=src_pad_mask,
layer_cache=layer_cache,
type="context",
)
output = self.feed_forward(self.drop(mid) + query)
return output, all_input
# return output
def _get_attn_subsequent_mask(self, size):
"""
Get an attention mask to avoid using the subsequent info.
Args:
size: int
Returns:
(`LongTensor`):
* subsequent_mask `[1 x size x size]`
"""
attn_shape = (1, size, size)
subsequent_mask = np.triu(np.ones(attn_shape), k=1).astype("uint8")
subsequent_mask = torch.from_numpy(subsequent_mask)
return subsequent_mask
class MultiHeadedAttention(nn.Module):
"""
Multi-Head Attention module from
"Attention is All You Need"
:cite:`DBLP:journals/corr/VaswaniSPUJGKP17`.
Similar to standard `dot` attention but uses
multiple attention distributions simulataneously
to select relevant items.
.. mermaid::
graph BT
A[key]
B[value]
C[query]
O[output]
subgraph Attn
D[Attn 1]
E[Attn 2]
F[Attn N]
end
A --> D
C --> D
A --> E
C --> E
A --> F
C --> F
D --> O
E --> O
F --> O
B --> O
Also includes several additional tricks.
Args:
head_count (int): number of parallel heads
model_dim (int): the dimension of keys/values/queries,
must be divisible by head_count
dropout (float): dropout parameter
"""
def __init__(self, head_count, model_dim, dropout=0.1, use_final_linear=True):
assert model_dim % head_count == 0
self.dim_per_head = model_dim // head_count
self.model_dim = model_dim
super().__init__()
self.head_count = head_count
self.linear_keys = nn.Linear(model_dim, head_count * self.dim_per_head)
self.linear_values = nn.Linear(model_dim, head_count * self.dim_per_head)
self.linear_query = nn.Linear(model_dim, head_count * self.dim_per_head)
self.softmax = nn.Softmax(dim=-1)
self.dropout = nn.Dropout(dropout)
self.use_final_linear = use_final_linear
if self.use_final_linear:
self.final_linear = nn.Linear(model_dim, model_dim)
def forward(
self,
key,
value,
query,
mask=None,
layer_cache=None,
type=None,
predefined_graph_1=None,
):
"""
Compute the context vector and the attention vectors.
Args:
key (`FloatTensor`): set of `key_len`
key vectors `[batch, key_len, dim]`
value (`FloatTensor`): set of `key_len`
value vectors `[batch, key_len, dim]`
query (`FloatTensor`): set of `query_len`
query vectors `[batch, query_len, dim]`
mask: binary mask indicating which keys have
non-zero attention `[batch, query_len, key_len]`
Returns:
(`FloatTensor`, `FloatTensor`) :
* output context vectors `[batch, query_len, dim]`
* one of the attention vectors `[batch, query_len, key_len]`
"""
batch_size = key.size(0)
dim_per_head = self.dim_per_head
head_count = self.head_count
def shape(x):
""" projection """
return x.view(batch_size, -1, head_count, dim_per_head).transpose(1, 2)
def unshape(x):
""" compute context """
return x.transpose(1, 2).contiguous().view(batch_size, -1, head_count * dim_per_head)
# 1) Project key, value, and query.
if layer_cache is not None:
if type == "self":
query, key, value = (
self.linear_query(query),
self.linear_keys(query),
self.linear_values(query),
)
key = shape(key)
value = shape(value)
if layer_cache is not None:
device = key.device
if layer_cache["self_keys"] is not None:
key = torch.cat((layer_cache["self_keys"].to(device), key), dim=2)
if layer_cache["self_values"] is not None:
value = torch.cat((layer_cache["self_values"].to(device), value), dim=2)
layer_cache["self_keys"] = key
layer_cache["self_values"] = value
elif type == "context":
query = self.linear_query(query)
if layer_cache is not None:
if layer_cache["memory_keys"] is None:
key, value = self.linear_keys(key), self.linear_values(value)
key = shape(key)
value = shape(value)
else:
key, value = (
layer_cache["memory_keys"],
layer_cache["memory_values"],
)
layer_cache["memory_keys"] = key
layer_cache["memory_values"] = value
else:
key, value = self.linear_keys(key), self.linear_values(value)
key = shape(key)
value = shape(value)
else:
key = self.linear_keys(key)
value = self.linear_values(value)
query = self.linear_query(query)
key = shape(key)
value = shape(value)
query = shape(query)
# 2) Calculate and scale scores.
query = query / math.sqrt(dim_per_head)
scores = torch.matmul(query, key.transpose(2, 3))
if mask is not None:
mask = mask.unsqueeze(1).expand_as(scores)
scores = scores.masked_fill(mask, -1e18)
# 3) Apply attention dropout and compute context vectors.
attn = self.softmax(scores)
if predefined_graph_1 is not None:
attn_masked = attn[:, -1] * predefined_graph_1
attn_masked = attn_masked / (torch.sum(attn_masked, 2).unsqueeze(2) + 1e-9)
attn = torch.cat([attn[:, :-1], attn_masked.unsqueeze(1)], 1)
drop_attn = self.dropout(attn)
if self.use_final_linear:
context = unshape(torch.matmul(drop_attn, value))
output = self.final_linear(context)
return output
else:
context = torch.matmul(drop_attn, value)
return context
class DecoderState(object):
"""Interface for grouping together the current state of a recurrent
decoder. In the simplest case just represents the hidden state of
the model. But can also be used for implementing various forms of
input_feeding and non-recurrent models.
Modules need to implement this to utilize beam search decoding.
"""
def detach(self):
""" Need to document this """
self.hidden = tuple([_.detach() for _ in self.hidden])
self.input_feed = self.input_feed.detach()
def beam_update(self, idx, positions, beam_size):
""" Need to document this """
for e in self._all:
sizes = e.size()
br = sizes[1]
if len(sizes) == 3:
sent_states = e.view(sizes[0], beam_size, br // beam_size, sizes[2])[:, :, idx]
else:
sent_states = e.view(sizes[0], beam_size, br // beam_size, sizes[2], sizes[3])[:, :, idx]
sent_states.data.copy_(sent_states.data.index_select(1, positions))
def map_batch_fn(self, fn):
raise NotImplementedError()
class TransformerDecoderState(DecoderState):
""" Transformer Decoder state base class """
def __init__(self, src):
"""
Args:
src (FloatTensor): a sequence of source words tensors
with optional feature tensors, of size (len x batch).
"""
self.src = src
self.previous_input = None
self.previous_layer_inputs = None
self.cache = None
@property
def _all(self):
"""
Contains attributes that need to be updated in self.beam_update().
"""
if self.previous_input is not None and self.previous_layer_inputs is not None:
return (self.previous_input, self.previous_layer_inputs, self.src)
else:
return (self.src,)
def detach(self):
if self.previous_input is not None:
self.previous_input = self.previous_input.detach()
if self.previous_layer_inputs is not None:
self.previous_layer_inputs = self.previous_layer_inputs.detach()
self.src = self.src.detach()
def update_state(self, new_input, previous_layer_inputs):
state = TransformerDecoderState(self.src)
state.previous_input = new_input
state.previous_layer_inputs = previous_layer_inputs
return state
def _init_cache(self, memory_bank, num_layers):
self.cache = {}
for l in range(num_layers):
layer_cache = {"memory_keys": None, "memory_values": None}
layer_cache["self_keys"] = None
layer_cache["self_values"] = None
self.cache["layer_{}".format(l)] = layer_cache
def repeat_beam_size_times(self, beam_size):
""" Repeat beam_size times along batch dimension. """
self.src = self.src.data.repeat(1, beam_size, 1)
def map_batch_fn(self, fn):
def _recursive_map(struct, batch_dim=0):
for k, v in struct.items():
if v is not None:
if isinstance(v, dict):
_recursive_map(v)
else:
struct[k] = fn(v, batch_dim)
self.src = fn(self.src, 0)
if self.cache is not None:
_recursive_map(self.cache)
def gelu(x):
return 0.5 * x * (1 + torch.tanh(math.sqrt(2 / math.pi) * (x + 0.044715 * torch.pow(x, 3))))
class PositionwiseFeedForward(nn.Module):
"""A two-layer Feed-Forward-Network with residual layer norm.
Args:
d_model (int): the size of input for the first-layer of the FFN.
d_ff (int): the hidden layer size of the second-layer
of the FNN.
dropout (float): dropout probability in :math:`[0, 1)`.
"""
def __init__(self, d_model, d_ff, dropout=0.1):
super().__init__()
self.w_1 = nn.Linear(d_model, d_ff)
self.w_2 = nn.Linear(d_ff, d_model)
self.layer_norm = nn.LayerNorm(d_model, eps=1e-6)
self.actv = gelu
self.dropout_1 = nn.Dropout(dropout)
self.dropout_2 = nn.Dropout(dropout)
def forward(self, x):
inter = self.dropout_1(self.actv(self.w_1(self.layer_norm(x))))
output = self.dropout_2(self.w_2(inter))
return output + x
#
# TRANSLATOR
# The following code is used to generate summaries using the
# pre-trained weights and beam search.
#
def build_predictor(args, tokenizer, symbols, model, logger=None):
# we should be able to refactor the global scorer a lot
scorer = GNMTGlobalScorer(args.alpha, length_penalty="wu")
translator = Translator(args, model, tokenizer, symbols, global_scorer=scorer, logger=logger)
return translator
class GNMTGlobalScorer(object):
"""
NMT re-ranking score from
"Google's Neural Machine Translation System" :cite:`wu2016google`
Args:
alpha (float): length parameter
beta (float): coverage parameter
"""
def __init__(self, alpha, length_penalty):
self.alpha = alpha
penalty_builder = PenaltyBuilder(length_penalty)
self.length_penalty = penalty_builder.length_penalty()
def score(self, beam, logprobs):
"""
Rescores a prediction based on penalty functions
"""
normalized_probs = self.length_penalty(beam, logprobs, self.alpha)
return normalized_probs
class PenaltyBuilder(object):
"""
Returns the Length and Coverage Penalty function for Beam Search.
Args:
length_pen (str): option name of length pen
cov_pen (str): option name of cov pen
"""
def __init__(self, length_pen):
self.length_pen = length_pen
def length_penalty(self):
if self.length_pen == "wu":
return self.length_wu
elif self.length_pen == "avg":
return self.length_average
else:
return self.length_none
"""
Below are all the different penalty terms implemented so far
"""
def length_wu(self, beam, logprobs, alpha=0.0):
"""
NMT length re-ranking score from
"Google's Neural Machine Translation System" :cite:`wu2016google`.
"""
modifier = ((5 + len(beam.next_ys)) ** alpha) / ((5 + 1) ** alpha)
return logprobs / modifier
def length_average(self, beam, logprobs, alpha=0.0):
"""
Returns the average probability of tokens in a sequence.
"""
return logprobs / len(beam.next_ys)
def length_none(self, beam, logprobs, alpha=0.0, beta=0.0):
"""
Returns unmodified scores.
"""
return logprobs
class Translator(object):
"""
Uses a model to translate a batch of sentences.
Args:
model (:obj:`onmt.modules.NMTModel`):
NMT model to use for translation
fields (dict of Fields): data fields
beam_size (int): size of beam to use
n_best (int): number of translations produced
max_length (int): maximum length output to produce
global_scores (:obj:`GlobalScorer`):
object to rescore final translations
copy_attn (bool): use copy attention during translation
beam_trace (bool): trace beam search for debugging
logger(logging.Logger): logger.
"""
def __init__(self, args, model, vocab, symbols, global_scorer=None, logger=None):
self.logger = logger
self.args = args
self.model = model
self.generator = self.model.generator
self.vocab = vocab
self.symbols = symbols
self.start_token = symbols["BOS"]
self.end_token = symbols["EOS"]
self.global_scorer = global_scorer
self.beam_size = args.beam_size
self.min_length = args.min_length
self.max_length = args.max_length
def translate(self, batch, step, attn_debug=False):
"""Generates summaries from one batch of data."""
self.model.eval()
with torch.no_grad():
batch_data = self.translate_batch(batch)
translations = self.from_batch(batch_data)
return translations
def translate_batch(self, batch, fast=False):
"""
Translate a batch of sentences.
Mostly a wrapper around :obj:`Beam`.
Args:
batch (:obj:`Batch`): a batch from a dataset object
fast (bool): enables fast beam search (may not support all features)
"""
with torch.no_grad():
return self._fast_translate_batch(batch, self.max_length, min_length=self.min_length)
# Where the beam search lives
# I have no idea why it is being called from the method above
def _fast_translate_batch(self, batch, max_length, min_length=0):
"""Beam Search using the encoder inputs contained in `batch`."""
# The batch object is funny
# Instead of just looking at the size of the arguments we encapsulate
# a size argument.
# Where is it defined?
beam_size = self.beam_size
batch_size = batch.batch_size
src = batch.src
segs = batch.segs
mask_src = batch.mask_src
src_features = self.model.bert(src, segs, mask_src)
dec_states = self.model.decoder.init_decoder_state(src, src_features, with_cache=True)
device = src_features.device
# Tile states and memory beam_size times.
dec_states.map_batch_fn(lambda state, dim: tile(state, beam_size, dim=dim))
src_features = tile(src_features, beam_size, dim=0)
batch_offset = torch.arange(batch_size, dtype=torch.long, device=device)
beam_offset = torch.arange(0, batch_size * beam_size, step=beam_size, dtype=torch.long, device=device)
alive_seq = torch.full([batch_size * beam_size, 1], self.start_token, dtype=torch.long, device=device)
# Give full probability to the first beam on the first step.
topk_log_probs = torch.tensor([0.0] + [float("-inf")] * (beam_size - 1), device=device).repeat(batch_size)
# Structure that holds finished hypotheses.
hypotheses = [[] for _ in range(batch_size)] # noqa: F812
results = {}
results["predictions"] = [[] for _ in range(batch_size)] # noqa: F812
results["scores"] = [[] for _ in range(batch_size)] # noqa: F812
results["gold_score"] = [0] * batch_size
results["batch"] = batch
for step in range(max_length):
decoder_input = alive_seq[:, -1].view(1, -1)
# Decoder forward.
decoder_input = decoder_input.transpose(0, 1)
dec_out, dec_states = self.model.decoder(decoder_input, src_features, dec_states, step=step)
# Generator forward.
log_probs = self.generator(dec_out.transpose(0, 1).squeeze(0))
vocab_size = log_probs.size(-1)
if step < min_length:
log_probs[:, self.end_token] = -1e20
# Multiply probs by the beam probability.
log_probs += topk_log_probs.view(-1).unsqueeze(1)
alpha = self.global_scorer.alpha
length_penalty = ((5.0 + (step + 1)) / 6.0) ** alpha
# Flatten probs into a list of possibilities.
curr_scores = log_probs / length_penalty
if self.args.block_trigram:
cur_len = alive_seq.size(1)
if cur_len > 3:
for i in range(alive_seq.size(0)):
fail = False
words = [int(w) for w in alive_seq[i]]
words = [self.vocab.ids_to_tokens[w] for w in words]
words = " ".join(words).replace(" ##", "").split()
if len(words) <= 3:
continue
trigrams = [(words[i - 1], words[i], words[i + 1]) for i in range(1, len(words) - 1)]
trigram = tuple(trigrams[-1])
if trigram in trigrams[:-1]:
fail = True
if fail:
curr_scores[i] = -10e20
curr_scores = curr_scores.reshape(-1, beam_size * vocab_size)
topk_scores, topk_ids = curr_scores.topk(beam_size, dim=-1)
# Recover log probs.
topk_log_probs = topk_scores * length_penalty
# Resolve beam origin and true word ids.
topk_beam_index = topk_ids.div(vocab_size)
topk_ids = topk_ids.fmod(vocab_size)
# Map beam_index to batch_index in the flat representation.
batch_index = topk_beam_index + beam_offset[: topk_beam_index.size(0)].unsqueeze(1)
select_indices = batch_index.view(-1)
# Append last prediction.
alive_seq = torch.cat([alive_seq.index_select(0, select_indices), topk_ids.view(-1, 1)], -1)
is_finished = topk_ids.eq(self.end_token)
if step + 1 == max_length:
is_finished.fill_(1)
# End condition is top beam is finished.
end_condition = is_finished[:, 0].eq(1)
# Save finished hypotheses.
if is_finished.any():
predictions = alive_seq.view(-1, beam_size, alive_seq.size(-1))
for i in range(is_finished.size(0)):
b = batch_offset[i]
if end_condition[i]:
is_finished[i].fill_(1)
finished_hyp = is_finished[i].nonzero().view(-1)
# Store finished hypotheses for this batch.
for j in finished_hyp:
hypotheses[b].append((topk_scores[i, j], predictions[i, j, 1:]))
# If the batch reached the end, save the n_best hypotheses.
if end_condition[i]:
best_hyp = sorted(hypotheses[b], key=lambda x: x[0], reverse=True)
score, pred = best_hyp[0]
results["scores"][b].append(score)
results["predictions"][b].append(pred)
non_finished = end_condition.eq(0).nonzero().view(-1)
# If all sentences are translated, no need to go further.
if len(non_finished) == 0:
break
# Remove finished batches for the next step.
topk_log_probs = topk_log_probs.index_select(0, non_finished)
batch_index = batch_index.index_select(0, non_finished)
batch_offset = batch_offset.index_select(0, non_finished)
alive_seq = predictions.index_select(0, non_finished).view(-1, alive_seq.size(-1))
# Reorder states.
select_indices = batch_index.view(-1)
src_features = src_features.index_select(0, select_indices)
dec_states.map_batch_fn(lambda state, dim: state.index_select(dim, select_indices))
return results
def from_batch(self, translation_batch):
batch = translation_batch["batch"]
assert len(translation_batch["gold_score"]) == len(translation_batch["predictions"])
batch_size = batch.batch_size
preds, _, _, tgt_str, src = (
translation_batch["predictions"],
translation_batch["scores"],
translation_batch["gold_score"],
batch.tgt_str,
batch.src,
)
translations = []
for b in range(batch_size):
pred_sents = self.vocab.convert_ids_to_tokens([int(n) for n in preds[b][0]])
pred_sents = " ".join(pred_sents).replace(" ##", "")
gold_sent = " ".join(tgt_str[b].split())
raw_src = [self.vocab.ids_to_tokens[int(t)] for t in src[b]][:500]
raw_src = " ".join(raw_src)
translation = (pred_sents, gold_sent, raw_src)
translations.append(translation)
return translations
def tile(x, count, dim=0):
"""
Tiles x on dimension dim count times.
"""
perm = list(range(len(x.size())))
if dim != 0:
perm[0], perm[dim] = perm[dim], perm[0]
x = x.permute(perm).contiguous()
out_size = list(x.size())
out_size[0] *= count
batch = x.size(0)
x = x.view(batch, -1).transpose(0, 1).repeat(count, 1).transpose(0, 1).contiguous().view(*out_size)
if dim != 0:
x = x.permute(perm).contiguous()
return x
#
# Optimizer for training. We keep this here in case we want to add
# a finetuning script.
#
class BertSumOptimizer(object):
"""Specific optimizer for BertSum.
As described in [1], the authors fine-tune BertSum for abstractive
summarization using two Adam Optimizers with different warm-up steps and
learning rate. They also use a custom learning rate scheduler.
[1] Liu, Yang, and Mirella Lapata. "Text summarization with pretrained encoders."
arXiv preprint arXiv:1908.08345 (2019).
"""
def __init__(self, model, lr, warmup_steps, beta_1=0.99, beta_2=0.999, eps=1e-8):
self.encoder = model.encoder
self.decoder = model.decoder
self.lr = lr
self.warmup_steps = warmup_steps
self.optimizers = {
"encoder": torch.optim.Adam(
model.encoder.parameters(),
lr=lr["encoder"],
betas=(beta_1, beta_2),
eps=eps,
),
"decoder": torch.optim.Adam(
model.decoder.parameters(),
lr=lr["decoder"],
betas=(beta_1, beta_2),
eps=eps,
),
}
self._step = 0
self.current_learning_rates = {}
def _update_rate(self, stack):
return self.lr[stack] * min(self._step ** (-0.5), self._step * self.warmup_steps[stack] ** (-1.5))
def zero_grad(self):
self.optimizer_decoder.zero_grad()
self.optimizer_encoder.zero_grad()
def step(self):
self._step += 1
for stack, optimizer in self.optimizers.items():
new_rate = self._update_rate(stack)
for param_group in optimizer.param_groups:
param_group["lr"] = new_rate
optimizer.step()
self.current_learning_rates[stack] = new_rate

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