/usr/local/lib/python3.6/site-packages/transformers
Edit: /usr/local/lib/python3.6/site-packages/transformers/generation_beam_search.py (40145B)
# coding=utf-8
# Copyright 2020 The HuggingFace Inc. team
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import warnings
from abc import ABC, abstractmethod
from collections import UserDict
from typing import List, Optional, Tuple
import numpy as np
import torch
from .generation_beam_constraints import Constraint, ConstraintListState
from .utils import add_start_docstrings
PROCESS_INPUTS_DOCSTRING = r"""
Args:
input_ids (`torch.LongTensor` of shape `(batch_size * num_beams, sequence_length)`):
Indices of input sequence tokens in the vocabulary.
Indices can be obtained using any class inheriting from [`PreTrainedTokenizer`]. See
[`PreTrainedTokenizer.encode`] and [`PreTrainedTokenizer.__call__`] for details.
[What are input IDs?](../glossary#input-ids)
next_scores (`torch.FloatTensor` of shape `(batch_size, 2 * num_beams)`):
Current scores of the top `2 * num_beams` non-finished beam hypotheses.
next_tokens (`torch.LongTensor` of shape `(batch_size, 2 * num_beams)`):
`input_ids` of the tokens corresponding to the top `2 * num_beams` non-finished beam hypotheses.
next_indices (`torch.LongTensor` of shape `(batch_size, 2 * num_beams)`):
Beam indices indicating to which beam hypothesis the `next_tokens` correspond.
pad_token_id (`int`, *optional*):
The id of the *padding* token.
eos_token_id (`int`, *optional*):
The id of the *end-of-sequence* token.
Return:
`UserDict`: A dictionary composed of the fields as defined above:
- **next_beam_scores** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Updated scores of all
non-finished beams.
- **next_beam_tokens** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Next tokens to be added
to the non-finished beam_hypotheses.
- **next_beam_indices** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Beam indices
indicating to which beam the next tokens shall be added.
"""
FINALIZE_INPUTS_DOCSTRING = r"""
Args:
input_ids (`torch.LongTensor` of shape `(batch_size * num_beams, sequence_length)`):
Indices of input sequence tokens in the vocabulary.
Indices can be obtained using any class inheriting from [`PreTrainedTokenizer`]. See
[`PreTrainedTokenizer.encode`] and [`PreTrainedTokenizer.__call__`] for details.
[What are input IDs?](../glossary#input-ids)
final_beam_scores (`torch.FloatTensor` of shape `(batch_size * num_beams)`):
The final scores of all non-finished beams.
final_beam_tokens (`torch.FloatTensor` of shape `(batch_size * num_beams)`):
The last tokens to be added to the non-finished beam_hypotheses.
final_beam_indices (`torch.FloatTensor` of shape `(batch_size * num_beams)`):
The beam indices indicating to which beam the `final_beam_tokens` shall be added.
pad_token_id (`int`, *optional*):
The id of the *padding* token.
eos_token_id (`int`, *optional*):
The id of the *end-of-sequence* token.
Return:
`torch.LongTensor` of shape `(batch_size * num_return_sequences, sequence_length)`: The generated sequences.
The second dimension (sequence_length) is either equal to `max_length` or shorter if all batches finished early
due to the `eos_token_id`.
"""
class BeamScorer(ABC):
"""
Abstract base class for all beam scorers that are used for [`~PreTrainedModel.beam_search`] and
[`~PreTrainedModel.beam_sample`].
"""
@abstractmethod
@add_start_docstrings(PROCESS_INPUTS_DOCSTRING)
def process(
self,
input_ids: torch.LongTensor,
next_scores: torch.FloatTensor,
next_tokens: torch.LongTensor,
next_indices: torch.LongTensor,
**kwargs
) -> Tuple[torch.Tensor]:
raise NotImplementedError("This is an abstract method.")
@abstractmethod
@add_start_docstrings(FINALIZE_INPUTS_DOCSTRING)
def finalize(
self,
input_ids: torch.LongTensor,
next_scores: torch.FloatTensor,
next_tokens: torch.LongTensor,
next_indices: torch.LongTensor,
max_length: int,
**kwargs
) -> torch.LongTensor:
raise NotImplementedError("This is an abstract method.")
class BeamSearchScorer(BeamScorer):
r"""
[`BeamScorer`] implementing standard beam search decoding.
Adapted in part from [Facebook's XLM beam search
code](https://github.com/facebookresearch/XLM/blob/9e6f6814d17be4fe5b15f2e6c43eb2b2d76daeb4/src/model/transformer.py#L529).
Reference for the diverse beam search algorithm and implementation [Ashwin Kalyan's DBS
implementation](https://github.com/ashwinkalyan/dbs/blob/master/dbs/beam_utils.lua)
Args:
batch_size (`int`):
Batch Size of `input_ids` for which standard beam search decoding is run in parallel.
max_length (`int`):
The maximum length of the sequence to be generated.
num_beams (`int`):
Number of beams for beam search.
device (`torch.device`):
Defines the device type (*e.g.*, `"cpu"` or `"cuda"`) on which this instance of `BeamSearchScorer` will be
allocated.
length_penalty (`float`, *optional*, defaults to 1.0):
Exponential penalty to the length. 1.0 means no penalty. Set to values < 1.0 in order to encourage the
model to generate shorter sequences, to a value > 1.0 in order to encourage the model to produce longer
sequences.
do_early_stopping (`bool`, *optional*, defaults to `False`):
Whether to stop the beam search when at least `num_beams` sentences are finished per batch or not.
num_beam_hyps_to_keep (`int`, *optional*, defaults to 1):
The number of beam hypotheses that shall be returned upon calling
[`~transformer.BeamSearchScorer.finalize`].
num_beam_groups (`int`):
Number of groups to divide `num_beams` into in order to ensure diversity among different groups of beams.
See [this paper](https://arxiv.org/pdf/1610.02424.pdf) for more details.
"""
def __init__(
self,
batch_size: int,
num_beams: int,
device: torch.device,
length_penalty: Optional[float] = 1.0,
do_early_stopping: Optional[bool] = False,
num_beam_hyps_to_keep: Optional[int] = 1,
num_beam_groups: Optional[int] = 1,
**kwargs,
):
self.num_beams = num_beams
self.device = device
self.length_penalty = length_penalty
self.do_early_stopping = do_early_stopping
self.num_beam_hyps_to_keep = num_beam_hyps_to_keep
self.num_beam_groups = num_beam_groups
self.group_size = self.num_beams // self.num_beam_groups
self._is_init = False
self._beam_hyps = [
BeamHypotheses(
num_beams=self.num_beams,
length_penalty=self.length_penalty,
early_stopping=self.do_early_stopping,
)
for _ in range(batch_size)
]
self._done = torch.tensor([False for _ in range(batch_size)], dtype=torch.bool, device=self.device)
if not isinstance(num_beams, int) or num_beams <= 1:
raise ValueError(
f"`num_beams` has to be an integer strictly greater than 1, but is {num_beams}. For `num_beams` == 1, one should make use of `greedy_search` instead."
)
if not isinstance(num_beam_groups, int) or (num_beam_groups > num_beams) or (num_beams % num_beam_groups != 0):
raise ValueError(
f"`num_beam_groups` has to be an integer smaller or equal than `num_beams` and `num_beams` "
f"has to be divisible by `num_beam_groups`, but is {num_beam_groups} with `num_beams` being {num_beams}."
)
if "max_length" in kwargs:
warnings.warn(
"Passing `max_length` to BeamSearchScorer is deprecated and has no effect. "
"`max_length` should be passed directly to `beam_search(...)`, `beam_sample(...)`"
", or `group_beam_search(...)`."
)
@property
def is_done(self) -> bool:
return self._done.all()
def process(
self,
input_ids: torch.LongTensor,
next_scores: torch.FloatTensor,
next_tokens: torch.LongTensor,
next_indices: torch.LongTensor,
pad_token_id: Optional[int] = None,
eos_token_id: Optional[int] = None,
) -> Tuple[torch.Tensor]:
cur_len = input_ids.shape[-1]
batch_size = len(self._beam_hyps)
if not (batch_size == (input_ids.shape[0] // self.group_size)):
if self.num_beam_groups > 1:
raise ValueError(
f"A group beam size of {input_ids.shape[0]} is used as the input, but a group beam "
f"size of {self.group_size} is expected by the beam scorer."
)
else:
raise ValueError(
f"A beam size of {input_ids.shape[0]} is used as the input, but a beam size of "
f"{self.group_size} is expected by the beam scorer."
)
device = input_ids.device
next_beam_scores = torch.zeros((batch_size, self.group_size), dtype=next_scores.dtype, device=device)
next_beam_tokens = torch.zeros((batch_size, self.group_size), dtype=next_tokens.dtype, device=device)
next_beam_indices = torch.zeros((batch_size, self.group_size), dtype=next_indices.dtype, device=device)
for batch_idx, beam_hyp in enumerate(self._beam_hyps):
if self._done[batch_idx]:
if self.num_beams < len(beam_hyp):
raise ValueError(f"Batch can only be done if at least {self.num_beams} beams have been generated")
if eos_token_id is None or pad_token_id is None:
raise ValueError("Generated beams >= num_beams -> eos_token_id and pad_token have to be defined")
# pad the batch
next_beam_scores[batch_idx, :] = 0
next_beam_tokens[batch_idx, :] = pad_token_id
next_beam_indices[batch_idx, :] = 0
continue
# next tokens for this sentence
beam_idx = 0
for beam_token_rank, (next_token, next_score, next_index) in enumerate(
zip(next_tokens[batch_idx], next_scores[batch_idx], next_indices[batch_idx])
):
batch_beam_idx = batch_idx * self.group_size + next_index
# add to generated hypotheses if end of sentence
if (eos_token_id is not None) and (next_token.item() == eos_token_id):
# if beam_token does not belong to top num_beams tokens, it should not be added
is_beam_token_worse_than_top_num_beams = beam_token_rank >= self.group_size
if is_beam_token_worse_than_top_num_beams:
continue
beam_hyp.add(
input_ids[batch_beam_idx].clone(),
next_score.item(),
)
else:
# add next predicted token since it is not eos_token
next_beam_scores[batch_idx, beam_idx] = next_score
next_beam_tokens[batch_idx, beam_idx] = next_token
next_beam_indices[batch_idx, beam_idx] = batch_beam_idx
beam_idx += 1
# once the beam for next step is full, don't add more tokens to it.
if beam_idx == self.group_size:
break
if beam_idx < self.group_size:
raise ValueError(
f"At most {self.group_size} tokens in {next_tokens[batch_idx]} can be equal to `eos_token_id: {eos_token_id}`. Make sure {next_tokens[batch_idx]} are corrected."
)
# Check if we are done so that we can save a pad step if all(done)
self._done[batch_idx] = self._done[batch_idx] or beam_hyp.is_done(
next_scores[batch_idx].max().item(), cur_len
)
return UserDict(
{
"next_beam_scores": next_beam_scores.view(-1),
"next_beam_tokens": next_beam_tokens.view(-1),
"next_beam_indices": next_beam_indices.view(-1),
}
)
def finalize(
self,
input_ids: torch.LongTensor,
final_beam_scores: torch.FloatTensor,
final_beam_tokens: torch.LongTensor,
final_beam_indices: torch.LongTensor,
max_length: int,
pad_token_id: Optional[int] = None,
eos_token_id: Optional[int] = None,
) -> Tuple[torch.LongTensor]:
batch_size = len(self._beam_hyps)
# finalize all open beam hypotheses and add to generated hypotheses
for batch_idx, beam_hyp in enumerate(self._beam_hyps):
if self._done[batch_idx]:
continue
# all open beam hypotheses are added to the beam hypothesis
# beam hypothesis class automatically keeps the best beams
for beam_id in range(self.num_beams):
batch_beam_idx = batch_idx * self.num_beams + beam_id
final_score = final_beam_scores[batch_beam_idx].item()
final_tokens = input_ids[batch_beam_idx]
beam_hyp.add(final_tokens, final_score)
# select the best hypotheses
sent_lengths = input_ids.new(batch_size * self.num_beam_hyps_to_keep)
best = []
best_scores = torch.zeros(batch_size * self.num_beam_hyps_to_keep, device=self.device, dtype=torch.float32)
# retrieve best hypotheses
for i, beam_hyp in enumerate(self._beam_hyps):
sorted_hyps = sorted(beam_hyp.beams, key=lambda x: x[0])
for j in range(self.num_beam_hyps_to_keep):
best_hyp_tuple = sorted_hyps.pop()
best_score = best_hyp_tuple[0]
best_hyp = best_hyp_tuple[1]
sent_lengths[self.num_beam_hyps_to_keep * i + j] = len(best_hyp)
# append to lists
best.append(best_hyp)
best_scores[i * self.num_beam_hyps_to_keep + j] = best_score
# prepare for adding eos
sent_lengths_max = sent_lengths.max().item() + 1
sent_max_len = min(sent_lengths_max, max_length) if max_length is not None else sent_lengths_max
decoded: torch.LongTensor = input_ids.new(batch_size * self.num_beam_hyps_to_keep, sent_max_len)
# shorter batches are padded if needed
if sent_lengths.min().item() != sent_lengths.max().item():
assert pad_token_id is not None, "`pad_token_id` has to be defined"
decoded.fill_(pad_token_id)
# fill with hypotheses and eos_token_id if the latter fits in
for i, hypo in enumerate(best):
decoded[i, : sent_lengths[i]] = hypo
if sent_lengths[i] < sent_max_len:
decoded[i, sent_lengths[i]] = eos_token_id
return UserDict(
{
"sequences": decoded,
"sequence_scores": best_scores,
}
)
class ConstrainedBeamSearchScorer(BeamScorer):
r"""
[`BeamScorer`] implementing constrained beam search decoding.
Args:
batch_size (`int`):
Batch Size of `input_ids` for which standard beam search decoding is run in parallel.
max_length (`int`):
The maximum length of the sequence to be generated.
num_beams (`int`):
Number of beams for beam search.
constraints (`List[Constraint]`):
A list of positive constraints represented as `Constraint` objects that must be fulfilled in the generation
output. For more information, the documentation of [`Constraint`] should be read.
device (`torch.device`):
Defines the device type (*e.g.*, `"cpu"` or `"cuda"`) on which this instance of `BeamSearchScorer` will be
allocated.
length_penalty (`float`, *optional*, defaults to 1.0):
Exponential penalty to the length. 1.0 means no penalty. Set to values < 1.0 in order to encourage the
model to generate shorter sequences, to a value > 1.0 in order to encourage the model to produce longer
sequences.
do_early_stopping (`bool`, *optional*, defaults to `False`):
Whether to stop the beam search when at least `num_beams` sentences are finished per batch or not.
num_beam_hyps_to_keep (`int`, *optional*, defaults to 1):
The number of beam hypotheses that shall be returned upon calling
[`~transformer.BeamSearchScorer.finalize`].
num_beam_groups (`int`):
Number of groups to divide `num_beams` into in order to ensure diversity among different groups of beams.
See [this paper](https://arxiv.org/pdf/1610.02424.pdf) for more details.
"""
def __init__(
self,
batch_size: int,
num_beams: int,
constraints: List[Constraint],
device: torch.device,
length_penalty: Optional[float] = 1.0,
do_early_stopping: Optional[bool] = False,
num_beam_hyps_to_keep: Optional[int] = 1,
num_beam_groups: Optional[int] = 1,
**kwargs,
):
self.num_beams = num_beams
self.device = device
self.length_penalty = length_penalty
self.do_early_stopping = do_early_stopping
self.num_beam_hyps_to_keep = num_beam_hyps_to_keep
self.num_beam_groups = num_beam_groups
self.group_size = self.num_beams // self.num_beam_groups
self.constraints = constraints
self._is_init = False
self._beam_hyps = [
BeamHypotheses(
num_beams=self.num_beams,
length_penalty=self.length_penalty,
early_stopping=self.do_early_stopping,
)
for _ in range(batch_size)
]
self._done = torch.tensor([False for _ in range(batch_size)], dtype=torch.bool, device=self.device)
if not isinstance(num_beams, int) or num_beams <= 1:
raise ValueError(
f"`num_beams` has to be an integer strictly greater than 1, but is {num_beams}. For `num_beams` == 1, one should make use of `greedy_search` instead."
)
if not isinstance(num_beam_groups, int) or (num_beam_groups > num_beams) or (num_beams % num_beam_groups != 0):
raise ValueError(
f"`num_beam_groups` has to be an integer smaller or equal than `num_beams` and `num_beams` "
f"has to be divisible by `num_beam_groups`, but is {num_beam_groups} with `num_beams` being {num_beams}."
)
if "max_length" in kwargs:
warnings.warn(
"Passing `max_length` to ConstrainedBeamSearchScorer is deprecated and has no effect. "
"`max_length` should be passed directly to `beam_search(...)`, `beam_sample(...)`"
", or `group_beam_search(...)`."
)
@property
def is_done(self) -> bool:
return self._done.all()
def make_constraint_states(self, n):
return [ConstraintListState([constraint.copy() for constraint in self.constraints]) for _ in range(n)]
def check_completes_constraints(self, sequence):
new_state = self.make_constraint_states(1)[0]
new_state.reset(sequence)
return new_state.completed
def process(
self,
input_ids: torch.LongTensor,
next_scores: torch.FloatTensor,
next_tokens: torch.LongTensor,
next_indices: torch.LongTensor,
scores_for_all_vocab: torch.FloatTensor,
pad_token_id: Optional[int] = None,
eos_token_id: Optional[int] = None,
) -> Tuple[torch.Tensor]:
r"""
Args:
input_ids (`torch.LongTensor` of shape `(batch_size * num_beams, sequence_length)`):
Indices of input sequence tokens in the vocabulary.
Indices can be obtained using any class inheriting from [`PreTrainedTokenizer`]. See
[`PreTrainedTokenizer.encode`] and [`PreTrainedTokenizer.__call__`] for details.
[What are input IDs?](../glossary#input-ids)
next_scores (`torch.FloatTensor` of shape `(batch_size, 2 * num_beams)`):
Current scores of the top `2 * num_beams` non-finished beam hypotheses.
next_tokens (`torch.LongTensor` of shape `(batch_size, 2 * num_beams)`):
`input_ids` of the tokens corresponding to the top `2 * num_beams` non-finished beam hypotheses.
next_indices (`torch.LongTensor` of shape `(batch_size, 2 * num_beams)`):
Beam indices indicating to which beam hypothesis the `next_tokens` correspond.
scores_for_all_vocab (`torch.FloatTensor` of shape `(batch_size * num_beams, sequence_length)`):
The scores of all tokens in the vocabulary for each of the beam hypotheses.
pad_token_id (`int`, *optional*):
The id of the *padding* token.
eos_token_id (`int`, *optional*):
The id of the *end-of-sequence* token.
Return:
`UserDict`: A dictionary composed of the fields as defined above:
- **next_beam_scores** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Updated scores of
all
non-finished beams.
- **next_beam_tokens** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Next tokens to be
added
to the non-finished beam_hypotheses.
- **next_beam_indices** (`torch.FloatTensor` of shape `(batch_size * num_beams)`) -- Beam indices
indicating to which beam the next tokens shall be added.
"""
cur_len = input_ids.shape[-1]
batch_size = len(self._beam_hyps)
if not (batch_size == (input_ids.shape[0] // self.group_size)):
if self.num_beam_groups > 1:
raise ValueError(
f"A group beam size of {input_ids.shape[0]} is used as the input, but a group beam "
f"size of {self.group_size} is expected by the beam scorer."
)
else:
raise ValueError(
f"A beam size of {input_ids.shape[0]} is used as the input, but a beam size of "
f"{self.group_size} is expected by the beam scorer."
)
device = input_ids.device
next_beam_scores = torch.zeros((batch_size, self.group_size), dtype=next_scores.dtype, device=device)
next_beam_tokens = torch.zeros((batch_size, self.group_size), dtype=next_tokens.dtype, device=device)
next_beam_indices = torch.zeros((batch_size, self.group_size), dtype=next_indices.dtype, device=device)
for batch_idx, beam_hyp in enumerate(self._beam_hyps):
if self._done[batch_idx]:
if self.num_beams < len(beam_hyp):
raise ValueError(f"Batch can only be done if at least {self.num_beams} beams have been generated")
if eos_token_id is None or pad_token_id is None:
raise ValueError("Generated beams >= num_beams -> eos_token_id and pad_token have to be defined")
# pad the batch
next_beam_scores[batch_idx, :] = 0
next_beam_tokens[batch_idx, :] = pad_token_id
next_beam_indices[batch_idx, :] = 0
continue
# next tokens for this sentence.
beam_idx = 0
for beam_token_rank, (next_token, next_score, next_index) in enumerate(
zip(next_tokens[batch_idx], next_scores[batch_idx], next_indices[batch_idx])
):
batch_beam_idx = batch_idx * self.group_size + next_index
# add to generated hypotheses if end of sentence
if (eos_token_id is not None) and (next_token.item() == eos_token_id):
# if beam_token does not belong to top num_beams tokens, it should not be added
is_beam_token_worse_than_top_num_beams = beam_token_rank >= self.group_size
if is_beam_token_worse_than_top_num_beams:
continue
completes_constraint = self.check_completes_constraints(input_ids[batch_beam_idx].cpu().tolist())
if completes_constraint:
beam_hyp.add(
input_ids[batch_beam_idx].clone(),
next_score.item(),
)
else:
# add next predicted token since it is not eos_token
next_beam_scores[batch_idx, beam_idx] = next_score
next_beam_tokens[batch_idx, beam_idx] = next_token
next_beam_indices[batch_idx, beam_idx] = batch_beam_idx
beam_idx += 1
# once the beam for next step is full, don't add more tokens to it.
if beam_idx == self.group_size:
break
new_scores, new_tokens, new_indices = self.step_sentence_constraint(
batch_idx,
input_ids,
scores_for_all_vocab,
next_beam_scores[batch_idx],
next_beam_tokens[batch_idx],
next_beam_indices[batch_idx],
)
next_beam_scores[batch_idx] = new_scores
next_beam_tokens[batch_idx] = new_tokens
next_beam_indices[batch_idx] = new_indices
if beam_idx < self.group_size:
raise ValueError(
f"At most {self.group_size} tokens in {next_tokens[batch_idx]} can be equal to `eos_token_id: {eos_token_id}`. Make sure {next_tokens[batch_idx]} are corrected."
)
# Check if we are done so that we can save a pad step if all(done)
self._done[batch_idx] = self._done[batch_idx] or beam_hyp.is_done(
next_scores[batch_idx].max().item(), cur_len
)
return UserDict(
{
"next_beam_scores": next_beam_scores.view(-1),
"next_beam_tokens": next_beam_tokens.view(-1),
"next_beam_indices": next_beam_indices.view(-1),
}
)
def step_sentence_constraint(
self,
batch_idx: int,
input_ids: torch.LongTensor,
vocab_scores: torch.FloatTensor,
sent_beam_scores: torch.FloatTensor,
sent_beam_tokens: torch.LongTensor,
sent_beam_indices: torch.LongTensor,
push_progress: bool = False,
):
# sent_beam_tokens are the next {num_beams} number of tokens that are under consideration for this beam
# (candidate next tokens)
# 1. Adding "advance_tokens"
# using ConstraintStateList.advance(), we propose new tokens to be added into this "candidate list" that will
# advance us in fulfilling the constraints.
# 2. Selecting best candidates such that we end up with highest probable candidates
# that fulfill our constraints.
orig_len = sent_beam_indices.size(0)
device = sent_beam_indices.device
# initialize states
topk_contraint_states = self.make_constraint_states(orig_len)
advance_constraint_states = self.make_constraint_states(orig_len)
sidx, eidx = batch_idx * orig_len, (batch_idx + 1) * orig_len
this_batch_input_ids = input_ids[sidx:eidx]
this_batch_token_scores = vocab_scores[sidx:eidx]
full_hypotheses = torch.cat((input_ids[sent_beam_indices], sent_beam_tokens.unsqueeze(-1)), dim=-1)
# need to make new hypothesis that advance the constraints
track_new = {"new_seqs": [], "new_states": [], "new_indices": [], "new_tokens": [], "new_scores": []}
for seq_idx, pre_seq in enumerate(this_batch_input_ids):
# pre_seq = ith sequence generated before this step.
# input_ids -> (topk) generic beam search best model next tokens
# -> (advance) constraints forcing the next token
# either way, we need to sort them into "banks" later, so store a "ConstraintListState" for all types of
# hypotheses.
topk_state = topk_contraint_states[seq_idx]
topk_state.reset(full_hypotheses[seq_idx].cpu().tolist())
advance_state = advance_constraint_states[seq_idx]
advance_state.reset(pre_seq.cpu().tolist())
if not advance_state.completed:
advance_tokens = torch.LongTensor(advance_state.advance()).to(device)
for advance_token in advance_tokens:
# since adding each `advance_token` leads to a different hypothesis, create new state instance.
new_state = advance_state.copy(stateful=True)
new_state.add(advance_token.cpu().tolist())
advance_seq = torch.cat((pre_seq, advance_token.unsqueeze(0)), -1).cpu().tolist()
if advance_seq not in track_new["new_seqs"]:
# prevent duplicates, which are basically bound to happen in this process.
track_new["new_seqs"].append(advance_seq)
track_new["new_indices"].append(sidx + seq_idx) # idx -> global idx across all the batches
track_new["new_tokens"].append(advance_token)
track_new["new_scores"].append(this_batch_token_scores[seq_idx].take(advance_token))
track_new["new_states"].append(new_state)
elif push_progress:
# Basically, `sent_beam_indices` often chooses very little among `input_ids` the generated sequences that
# actually fulfill our constraints. For example, let constraints == ["loves pies"] and
# pre_seq_1 = "The child loves pies and" pre_seq_2 = "The child plays in the playground and"
# Without this step, if `sent_beam_indices` is something like [1,1], then
# 1. `pre_seq_1` won't be added to the list of (topk) hypothesis since it's not in the indices and
# 2. it won't be added to the list of (advance) hypothesis since it's completed already. (this is
# the else part of `if constraints_completed[seq_idx]`)
# 3. it ends up simply getting removed from consideration.
# #3 might be fine and actually desired, since it's likely that it's a low-probability output anyways,
# especially if it's not in the list of `sent_beam_indices`. But this often leads to lengthened beam
# search times, since completed sequences keep getting removed after all this effort for constrained
# generation.
# Here, we basically take `pre_seq_1` and to "push" it into the considered list of hypotheses, by simply
# appending the next likely token in the vocabulary and adding it to the list of hypotheses.
new_score, new_token = torch.max(this_batch_token_scores[seq_idx], 0) # some next probable token
advance_seq = torch.cat((pre_seq, new_token.unsqueeze(0)), -1)
advance_state = advance_constraint_states[seq_idx]
advance_seq = advance_seq.cpu().tolist()
advance_state.reset(advance_seq)
if advance_seq not in track_new["new_seqs"]:
# but still don't want to have duplicates
track_new["new_seqs"].append(advance_seq)
track_new["new_indices"].append(seq_idx)
track_new["new_tokens"].append(new_token)
track_new["new_scores"].append(new_score)
track_new["new_states"].append(advance_state)
if len(track_new["new_indices"]) > 0:
new_indices = torch.tensor(track_new["new_indices"]).to(device)
new_tokens = torch.stack(track_new["new_tokens"]).to(device)
new_scores = torch.stack(track_new["new_scores"]).to(device)
all_states = topk_contraint_states + track_new["new_states"]
all_tokens = torch.cat((sent_beam_tokens, new_tokens), -1)
all_scores = torch.cat((sent_beam_scores, new_scores), -1)
all_banks = torch.tensor([one.get_bank() for one in all_states]).to(device)
zipped = all_banks * 100 + all_scores
indices = zipped.sort(descending=True).indices
sorted_banks = all_banks[indices]
# Then we end up with {sorted among bank C}, {sorted among bank C-1}, ..., {sorted among bank 0}
counter = -1
cur_bank = sorted_banks[0]
increments = []
for bank in sorted_banks:
if bank == cur_bank:
counter += 1
else:
counter = 0
cur_bank = bank
increments.append(counter)
rearrangers = torch.tensor(np.argsort(increments, kind="mergesort"))
indices = indices[rearrangers][:orig_len]
sent_beam_scores = all_scores[indices]
sent_beam_tokens = all_tokens[indices]
sent_beam_indices = torch.cat((sent_beam_indices, new_indices))[indices]
return sent_beam_scores, sent_beam_tokens, sent_beam_indices
def finalize(
self,
input_ids: torch.LongTensor,
final_beam_scores: torch.FloatTensor,
final_beam_tokens: torch.LongTensor,
final_beam_indices: torch.LongTensor,
max_length: int,
pad_token_id: Optional[int] = None,
eos_token_id: Optional[int] = None,
) -> Tuple[torch.LongTensor]:
batch_size = len(self._beam_hyps)
# finalize all open beam hypotheses and add to generated hypotheses
for batch_idx, beam_hyp in enumerate(self._beam_hyps):
if self._done[batch_idx]:
continue
# all open beam hypotheses are added to the beam hypothesis
# beam hypothesis class automatically keeps the best beams
ids_collect = []
for beam_id in range(self.num_beams):
batch_beam_idx = batch_idx * self.num_beams + beam_id
final_score = final_beam_scores[batch_beam_idx].item()
final_tokens = input_ids[batch_beam_idx]
completes_constraint = self.check_completes_constraints(final_tokens.cpu().tolist())
if completes_constraint:
beam_hyp.add(final_tokens, final_score)
ids_collect.append(beam_id)
# due to overly complex constraints or other factors, sometimes we can't gaurantee a successful
# generation. In these cases we simply return the highest scoring outputs.
if len(ids_collect) < self.num_beam_hyps_to_keep:
for beam_id in range(self.num_beams):
if beam_id not in ids_collect:
batch_beam_idx = batch_idx * self.num_beams + beam_id
final_score = final_beam_scores[batch_beam_idx].item()
final_tokens = input_ids[batch_beam_idx]
beam_hyp.add(final_tokens, final_score)
if len(ids_collect) >= self.num_beam_hyps_to_keep:
break
# select the best hypotheses
sent_lengths = input_ids.new(batch_size * self.num_beam_hyps_to_keep)
best = []
best_scores = torch.zeros(batch_size * self.num_beam_hyps_to_keep, device=self.device, dtype=torch.float32)
# retrieve best hypotheses
for i, beam_hyp in enumerate(self._beam_hyps):
sorted_hyps = sorted(beam_hyp.beams, key=lambda x: x[0])
for j in range(self.num_beam_hyps_to_keep):
best_hyp_tuple = sorted_hyps.pop()
best_score = best_hyp_tuple[0]
best_hyp = best_hyp_tuple[1]
sent_lengths[self.num_beam_hyps_to_keep * i + j] = len(best_hyp)
# append to lists
best.append(best_hyp)
best_scores[i * self.num_beam_hyps_to_keep + j] = best_score
# prepare for adding eos
sent_lengths_max = sent_lengths.max().item() + 1
sent_max_len = min(sent_lengths_max, max_length) if max_length is not None else sent_lengths_max
decoded: torch.LongTensor = input_ids.new(batch_size * self.num_beam_hyps_to_keep, sent_max_len)
# shorter batches are padded if needed
if sent_lengths.min().item() != sent_lengths.max().item():
assert pad_token_id is not None, "`pad_token_id` has to be defined"
decoded.fill_(pad_token_id)
# fill with hypotheses and eos_token_id if the latter fits in
for i, hypo in enumerate(best):
decoded[i, : sent_lengths[i]] = hypo
if sent_lengths[i] < sent_max_len:
decoded[i, sent_lengths[i]] = eos_token_id
return UserDict(
{
"sequences": decoded,
"sequence_scores": best_scores,
}
)
class BeamHypotheses:
def __init__(self, num_beams: int, length_penalty: float, early_stopping: bool):
"""
Initialize n-best list of hypotheses.
"""
self.length_penalty = length_penalty
self.early_stopping = early_stopping
self.num_beams = num_beams
self.beams = []
self.worst_score = 1e9
def __len__(self):
"""
Number of hypotheses in the list.
"""
return len(self.beams)
def add(self, hyp: torch.LongTensor, sum_logprobs: float):
"""
Add a new hypothesis to the list.
"""
score = sum_logprobs / (hyp.shape[-1] ** self.length_penalty)
if len(self) < self.num_beams or score > self.worst_score:
self.beams.append((score, hyp))
if len(self) > self.num_beams:
sorted_next_scores = sorted([(s, idx) for idx, (s, _) in enumerate(self.beams)])
del self.beams[sorted_next_scores[0][1]]
self.worst_score = sorted_next_scores[1][0]
else:
self.worst_score = min(score, self.worst_score)
def is_done(self, best_sum_logprobs: float, cur_len: int) -> bool:
"""
If there are enough hypotheses and that none of the hypotheses being generated can become better than the worst
one in the heap, then we are done with this sentence.
"""
if len(self) < self.num_beams:
return False
elif self.early_stopping:
return True
else:
cur_score = best_sum_logprobs / cur_len**self.length_penalty
ret = self.worst_score >= cur_score
return ret