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# 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 inspect
import math
from abc import ABC
from typing import Callable, Iterable, List
import numpy as np
import torch
from .file_utils import add_start_docstrings
LOGITS_PROCESSOR_INPUTS_DOCSTRING = r"""
Args:
input_ids (:obj:`torch.LongTensor` of shape :obj:`(batch_size, sequence_length)`):
Indices of input sequence tokens in the vocabulary.
Indices can be obtained using :class:`~transformers.BertTokenizer`. See
:meth:`transformers.PreTrainedTokenizer.encode` and :meth:`transformers.PreTrainedTokenizer.__call__` for
details.
`What are input IDs? <../glossary.html#input-ids>`__
scores (:obj:`torch.FloatTensor` of shape :obj:`(batch_size, config.vocab_size)`):
Prediction scores of a language modeling head. These can be scores for each vocabulary token before SoftMax
or scores for each vocabulary token after SoftMax.
kwargs:
Additional logits processor specific kwargs.
Return:
:obj:`torch.FloatTensor` of shape :obj:`(batch_size, config.vocab_size)`: The processed prediction scores.
"""
class LogitsProcessor(ABC):
"""Abstract base class for all logit processors that can be applied during generation."""
@add_start_docstrings(LOGITS_PROCESSOR_INPUTS_DOCSTRING)
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
"""Torch method for processing logits."""
raise NotImplementedError(
f"{self.__class__} is an abstract class. Only classes inheriting this class can be called."
)
class LogitsWarper(ABC):
"""Abstract base class for all logit warpers that can be applied during generation with multinomial sampling."""
@add_start_docstrings(LOGITS_PROCESSOR_INPUTS_DOCSTRING)
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
"""Torch method for warping logits."""
raise NotImplementedError(
f"{self.__class__} is an abstract class. Only classes inheriting this class can be called."
)
class LogitsProcessorList(list):
"""
This class can be used to create a list of :class:`~transformers.LogitsProcessor` or
:class:`~transformers.LogitsWarper` to subsequently process a :obj:`scores` input tensor. This class inherits from
list and adds a specific `__call__` method to apply each :class:`~transformers.LogitsProcessor` or
:class:`~transformers.LogitsProcessor` to the inputs.
"""
@add_start_docstrings(LOGITS_PROCESSOR_INPUTS_DOCSTRING)
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor, **kwargs) -> torch.FloatTensor:
for processor in self:
function_args = inspect.signature(processor.__call__).parameters
if len(function_args) > 2:
assert all(
arg in kwargs for arg in list(function_args.keys())[2:]
), f"Make sure that all the required parameters: {list(function_args.keys())} for {processor.__class__} are passed to the logits processor."
scores = processor(input_ids, scores, **kwargs)
else:
scores = processor(input_ids, scores)
return scores
class MinLengthLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` enforcing a min-length by setting EOS probability to 0.
Args:
min_length (:obj:`int`):
The minimum length below which the score of :obj:`eos_token_id` is set to :obj:`-float("Inf")`.
eos_token_id (:obj:`int`):
The id of the `end-of-sequence` token.
"""
def __init__(self, min_length: int, eos_token_id: int):
if not isinstance(min_length, int) or min_length < 0:
raise ValueError(f"`min_length` has to be a positive integer, but is {min_length}")
if not isinstance(eos_token_id, int) or eos_token_id < 0:
raise ValueError(f"`eos_token_id` has to be a positive integer, but is {eos_token_id}")
self.min_length = min_length
self.eos_token_id = eos_token_id
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
cur_len = input_ids.shape[-1]
if cur_len < self.min_length:
scores[:, self.eos_token_id] = -float("inf")
return scores
class TemperatureLogitsWarper(LogitsWarper):
r"""
:class:`transformers.LogitsWarper` for temperature (exponential scaling output probability distribution).
Args:
temperature (:obj:`float`):
The value used to module the logits distribution.
"""
def __init__(self, temperature: float):
if not isinstance(temperature, float) or not (temperature > 0):
raise ValueError(f"`temperature` has to be a strictly positive float, but is {temperature}")
self.temperature = temperature
def __call__(self, input_ids: torch.Tensor, scores: torch.Tensor) -> torch.Tensor:
scores = scores / self.temperature
return scores
class RepetitionPenaltyLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` enforcing an exponential penalty on repeated sequences.
Args:
repetition_penalty (:obj:`float`):
The parameter for repetition penalty. 1.0 means no penalty. See `this paper
<https://arxiv.org/pdf/1909.05858.pdf>`__ for more details.
"""
def __init__(self, penalty: float):
if not isinstance(penalty, float) or not (penalty > 0):
raise ValueError(f"`penalty` has to be a strictly positive float, but is {penalty}")
self.penalty = penalty
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
score = torch.gather(scores, 1, input_ids)
# if score < 0 then repetition penalty has to be multiplied to reduce the previous token probability
score = torch.where(score < 0, score * self.penalty, score / self.penalty)
scores.scatter_(1, input_ids, score)
return scores
class TopPLogitsWarper(LogitsWarper):
"""
:class:`transformers.LogitsWarper` that performs top-p, i.e. restricting to top tokens summing to prob_cut_off <=
prob_cut_off.
Args:
top_p (:obj:`float`):
If set to < 1, only the most probable tokens with probabilities that add up to :obj:`top_p` or higher are
kept for generation.
filter_value (:obj:`float`, `optional`, defaults to :obj:`-float("Inf")`):
All filtered values will be set to this float value.
min_tokens_to_keep (:obj:`int`, `optional`, defaults to 1):
Minimum number of tokens that cannot be filtered.
"""
def __init__(self, top_p: float, filter_value: float = -float("Inf"), min_tokens_to_keep: int = 1):
if not isinstance(top_p, float) or (top_p < 0 or top_p > 1.0):
raise ValueError(f"`top_p` has to be a float > 0 and < 1, but is {top_p}")
self.top_p = top_p
self.filter_value = filter_value
self.min_tokens_to_keep = min_tokens_to_keep
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
sorted_logits, sorted_indices = torch.sort(scores, descending=True)
cumulative_probs = sorted_logits.softmax(dim=-1).cumsum(dim=-1)
# Remove tokens with cumulative top_p above the threshold (token with 0 are kept)
sorted_indices_to_remove = cumulative_probs > self.top_p
if self.min_tokens_to_keep > 1:
# Keep at least min_tokens_to_keep (set to min_tokens_to_keep-1 because we add the first one below)
sorted_indices_to_remove[..., : self.min_tokens_to_keep - 1] = 0
# Shift the indices to the right to keep also the first token above the threshold
sorted_indices_to_remove[..., 1:] = sorted_indices_to_remove[..., :-1].clone()
sorted_indices_to_remove[..., 0] = 0
# scatter sorted tensors to original indexing
indices_to_remove = sorted_indices_to_remove.scatter(1, sorted_indices, sorted_indices_to_remove)
scores = scores.masked_fill(indices_to_remove, self.filter_value)
return scores
class TopKLogitsWarper(LogitsWarper):
r"""
:class:`transformers.LogitsWarper` that performs top-k, i.e. restricting to the k highest probability elements.
Args:
top_k (:obj:`int`):
The number of highest probability vocabulary tokens to keep for top-k-filtering.
filter_value (:obj:`float`, `optional`, defaults to :obj:`-float("Inf")`):
All filtered values will be set to this float value.
min_tokens_to_keep (:obj:`int`, `optional`, defaults to 1):
Minimum number of tokens that cannot be filtered.
"""
def __init__(self, top_k: int, filter_value: float = -float("Inf"), min_tokens_to_keep: int = 1):
if not isinstance(top_k, int) or top_k <= 0:
raise ValueError(f"`top_k` has to be a strictly positive integer, but is {top_k}")
self.top_k = top_k
self.filter_value = filter_value
self.min_tokens_to_keep = min_tokens_to_keep
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
top_k = min(max(self.top_k, self.min_tokens_to_keep), scores.size(-1)) # Safety check
# Remove all tokens with a probability less than the last token of the top-k
indices_to_remove = scores < torch.topk(scores, top_k)[0][..., -1, None]
scores = scores.masked_fill(indices_to_remove, self.filter_value)
return scores
def _get_ngrams(ngram_size: int, prev_input_ids: torch.Tensor, num_hypos: int):
generated_ngrams = [{} for _ in range(num_hypos)]
for idx in range(num_hypos):
gen_tokens = prev_input_ids[idx].tolist()
generated_ngram = generated_ngrams[idx]
for ngram in zip(*[gen_tokens[i:] for i in range(ngram_size)]):
prev_ngram_tuple = tuple(ngram[:-1])
generated_ngram[prev_ngram_tuple] = generated_ngram.get(prev_ngram_tuple, []) + [ngram[-1]]
return generated_ngrams
def _get_generated_ngrams(banned_ngrams, prev_input_ids, ngram_size, cur_len):
# Before decoding the next token, prevent decoding of ngrams that have already appeared
start_idx = cur_len + 1 - ngram_size
ngram_idx = tuple(prev_input_ids[start_idx:cur_len].tolist())
return banned_ngrams.get(ngram_idx, [])
def _calc_banned_ngram_tokens(
ngram_size: int, prev_input_ids: torch.Tensor, num_hypos: int, cur_len: int
) -> List[Iterable[int]]:
"""Copied from fairseq for no_repeat_ngram in beam_search"""
if cur_len + 1 < ngram_size:
# return no banned tokens if we haven't generated no_repeat_ngram_size tokens yet
return [[] for _ in range(num_hypos)]
generated_ngrams = _get_ngrams(ngram_size, prev_input_ids, num_hypos)
banned_tokens = [
_get_generated_ngrams(generated_ngrams[hypo_idx], prev_input_ids[hypo_idx], ngram_size, cur_len)
for hypo_idx in range(num_hypos)
]
return banned_tokens
class NoRepeatNGramLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` that enforces no repetition of n-grams. See `Fairseq
<https://github.com/pytorch/fairseq/blob/a07cb6f40480928c9e0548b737aadd36ee66ac76/fairseq/sequence_generator.py#L345>`__.
Args:
ngram_size (:obj:`int`):
All ngrams of size :obj:`ngram_size` can only occur once.
"""
def __init__(self, ngram_size: int):
if not isinstance(ngram_size, int) or ngram_size <= 0:
raise ValueError(f"`ngram_size` has to be a strictly positive integer, but is {ngram_size}")
self.ngram_size = ngram_size
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
num_batch_hypotheses = scores.shape[0]
cur_len = input_ids.shape[-1]
banned_batch_tokens = _calc_banned_ngram_tokens(self.ngram_size, input_ids, num_batch_hypotheses, cur_len)
for i, banned_tokens in enumerate(banned_batch_tokens):
scores[i, banned_tokens] = -float("inf")
return scores
class EncoderNoRepeatNGramLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` that enforces no repetition of encoder input ids n-grams for the decoder ids.
See `ParlAI <https://github.com/facebookresearch/ParlAI/blob/master/parlai/core/torch_generator_agent.py#L1350>`__.
Args:
encoder_ngram_size (:obj:`int`):
All ngrams of size :obj:`ngram_size` can only occur within the encoder input ids.
encoder_input_ids (:obj:`int`):
The encoder_input_ids that should not be repeated within the decoder ids.
"""
def __init__(self, encoder_ngram_size: int, encoder_input_ids: torch.LongTensor):
if not isinstance(encoder_ngram_size, int) or encoder_ngram_size <= 0:
raise ValueError(
f"`encoder_ngram_size` has to be a strictly positive integer, but is {encoder_ngram_size}"
)
self.ngram_size = encoder_ngram_size
if len(encoder_input_ids.shape) == 1:
encoder_input_ids = encoder_input_ids.unsqueeze(0)
self.batch_size = encoder_input_ids.shape[0]
self.generated_ngrams = _get_ngrams(encoder_ngram_size, encoder_input_ids, self.batch_size)
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
# B x num_beams
num_hypos = scores.shape[0]
num_beams = num_hypos // self.batch_size
cur_len = input_ids.shape[-1]
banned_batch_tokens = [
_get_generated_ngrams(
self.generated_ngrams[hypo_idx // num_beams], input_ids[hypo_idx], self.ngram_size, cur_len
)
for hypo_idx in range(num_hypos)
]
for i, banned_tokens in enumerate(banned_batch_tokens):
scores[i, banned_tokens] = -float("inf")
return scores
class NoBadWordsLogitsProcessor(LogitsProcessor):
"""
:class:`transformers.LogitsProcessor` that enforces that specified sequences will never be sampled.
Args:
bad_words_ids (:obj:`List[List[int]]`):
List of list of token ids that are not allowed to be generated. In order to get the tokens of the words
that should not appear in the generated text, use :obj:`tokenizer(bad_word,
add_prefix_space=True).input_ids`.
eos_token_id (:obj:`int`):
The id of the `end-of-sequence` token.
"""
def __init__(self, bad_words_ids: Iterable[Iterable[int]], eos_token_id: int):
if not isinstance(bad_words_ids, List) or len(bad_words_ids) == 0:
raise ValueError(f"`bad_words_ids` has to be a non-emtpy list, but is {bad_words_ids}.")
if any(not isinstance(bad_word_ids, list) for bad_word_ids in bad_words_ids):
raise ValueError(f"`bad_words_ids` has to be a list of lists, but is {bad_words_ids}.")
if any(
any((not isinstance(token_id, (int, np.integer)) or token_id < 0) for token_id in bad_word_ids)
for bad_word_ids in bad_words_ids
):
raise ValueError(
f"Each list in `bad_words_ids` has to be a list of positive integers, but is {bad_words_ids}."
)
self.bad_words_ids = list(filter(lambda bad_token_seq: bad_token_seq != [eos_token_id], bad_words_ids))
for banned_token_seq in self.bad_words_ids:
assert len(banned_token_seq) > 0, "Banned words token sequences {} cannot have an empty list".format(
bad_words_ids
)
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
banned_tokens = self._calc_banned_bad_words_ids(input_ids)
scores = self._set_scores_to_inf_for_banned_tokens(scores, banned_tokens)
return scores
def _tokens_match(self, prev_tokens: torch.LongTensor, tokens: List[int]) -> bool:
if len(tokens) == 0:
# if bad word tokens is just one token always ban it
return True
elif len(tokens) > len(prev_tokens):
# if bad word tokens are longer then prev input_ids they can't be equal
return False
elif prev_tokens[-len(tokens) :].tolist() == tokens:
# if tokens match
return True
else:
return False
def _calc_banned_bad_words_ids(self, prev_input_ids: Iterable[int]) -> Iterable[int]:
banned_tokens = []
for prev_input_ids_slice in prev_input_ids:
banned_tokens_slice = []
for banned_token_seq in self.bad_words_ids:
if self._tokens_match(prev_input_ids_slice, banned_token_seq[:-1]) is False:
# if tokens do not match continue
continue
banned_tokens_slice.append(banned_token_seq[-1])
banned_tokens.append(banned_tokens_slice)
return banned_tokens
def _set_scores_to_inf_for_banned_tokens(self, scores: torch.Tensor, banned_tokens: List[List[int]]) -> None:
"""
Modifies the scores in place by setting the banned token positions to `-inf`. Banned token is expected to be a
list of list of banned tokens to ban in the format [[batch index, vocabulary position],...
Args:
scores: logits distribution of shape (batch size, vocabulary size)
banned_tokens: list of list of tokens to ban of length (batch_size)
"""
banned_mask_list = []
for idx, batch_banned_tokens in enumerate(banned_tokens):
for token in batch_banned_tokens:
banned_mask_list.append([idx, token])
if not banned_mask_list:
return scores
banned_mask = torch.LongTensor(banned_mask_list)
indices = torch.ones(len(banned_mask))
# A sparse tensor is generated from a list of coordinates: [[0, 1], [0, 2], [2, 0]]. A conversion to dense tensor generates:
# [ 0 1 1 ]
# [ 0 0 0 ]
# [ 1 0 0 ]
banned_mask = (
torch.sparse.LongTensor(banned_mask.t(), indices, scores.size()).to(scores.device).to_dense().bool()
)
scores = scores.masked_fill(banned_mask, -float("inf"))
return scores
class PrefixConstrainedLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` that enforces contrained generation and is useful for prefix-conditioned
constrained generation. See `Autoregressive Entity Retrieval <https://arxiv.org/abs/2010.00904>`__ for more
information.
Args:
prefix_allowed_tokens_fn: (:obj:`Callable[[int, torch.Tensor], List[int]]`):
This function constraints the beam search to allowed tokens only at each step. This function takes 2
arguments :obj:`inputs_ids` and the batch ID :obj:`batch_id`. It has to return a list with the allowed
tokens for the next generation step conditioned on the previously generated tokens :obj:`inputs_ids` and
the batch ID :obj:`batch_id`.
"""
def __init__(self, prefix_allowed_tokens_fn: Callable[[int, torch.Tensor], List[int]], num_beams: int):
self._prefix_allowed_tokens_fn = prefix_allowed_tokens_fn
self._num_beams = num_beams
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
mask = torch.full_like(scores, -math.inf)
for batch_id, beam_sent in enumerate(input_ids.view(-1, self._num_beams, input_ids.shape[-1])):
for beam_id, sent in enumerate(beam_sent):
mask[batch_id * self._num_beams + beam_id, self._prefix_allowed_tokens_fn(batch_id, sent)] = 0
return scores + mask
class HammingDiversityLogitsProcessor(LogitsProcessor):
r"""
:class:`transformers.LogitsProcessor` that enforces diverse beam search. Note that this logits processor is only
effective for :meth:`transformers.PretrainedModel.group_beam_search`. See `Diverse Beam Search: Decoding Diverse
Solutions from Neural Sequence Models <https://arxiv.org/pdf/1610.02424.pdf>`__ for more details.
Args:
diversity_penalty (:obj:`float`):
This value is subtracted from a beam's score if it generates a token same as any beam from other group at a
particular time. Note that :obj:`diversity_penalty` is only effective if ``group beam search`` is enabled.
num_beams (:obj:`int`):
Number of beams used for group beam search. See `this paper <https://arxiv.org/pdf/1610.02424.pdf>`__ for
more details.
num_beam_groups (:obj:`int`):
Number of groups to divide :obj:`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, diversity_penalty: float, num_beams: int, num_beam_groups: int):
if not isinstance(diversity_penalty, float) or (not diversity_penalty > 0.0):
raise ValueError("`diversity_penalty` should be a float strictly larger than 0.")
self._diversity_penalty = diversity_penalty
if not isinstance(num_beams, int) or num_beams < 2:
raise ValueError("`num_beams` should be an integer strictly larger than 1.")
self._num_beams = num_beams
if not isinstance(num_beam_groups, int) or num_beam_groups < 2:
raise ValueError("`num_beam_groups` should be an integer strictly larger than 1.")
if num_beam_groups > num_beams:
raise ValueError("`beam_groups` has to be smaller or equal to `num_beams`.")
self._num_sub_beams = num_beams // num_beam_groups
def __call__(
self,
input_ids: torch.LongTensor,
scores: torch.FloatTensor,
current_tokens: torch.LongTensor,
beam_group_idx: int,
) -> torch.FloatTensor:
# hamming diversity: penalise using same token in current group which was used in previous groups at
# the same time step
batch_size = current_tokens.shape[0] // self._num_beams
group_start_idx = beam_group_idx * self._num_sub_beams
group_end_idx = min(group_start_idx + self._num_sub_beams, self._num_beams)
group_size = group_end_idx - group_start_idx
vocab_size = scores.shape[-1]
if group_start_idx == 0:
return scores
for batch_idx in range(batch_size):
# predicted tokens of last time step of previous groups
previous_group_tokens = current_tokens[
batch_idx * self._num_beams : batch_idx * self._num_beams + group_start_idx
]
token_frequency = torch.bincount(previous_group_tokens, minlength=vocab_size).to(scores.device)
scores[batch_idx * group_size : (batch_idx + 1) * group_size] -= self._diversity_penalty * token_frequency
return scores
class ForcedBOSTokenLogitsProcessor(LogitsProcessor):
r"""
:class:`~transformers.LogitsProcessor` that enforces the specified token as the first generated token.
Args:
bos_token_id (:obj:`int`):
The id of the token to force as the first generated token.
"""
def __init__(self, bos_token_id: int):
self.bos_token_id = bos_token_id
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
cur_len = input_ids.shape[-1]
if cur_len == 1:
num_tokens = scores.shape[1]
scores[:, [i for i in range(num_tokens) if i != self.bos_token_id]] = -float("inf")
scores[:, self.bos_token_id] = 0
return scores
class ForcedEOSTokenLogitsProcessor(LogitsProcessor):
r"""
:class:`~transformers.LogitsProcessor` that enforces the specified token as the last generated token when
:obj:`max_length` is reached.
Args:
max_length (:obj:`int`):
The maximum length of the sequence to be generated.
eos_token_id (:obj:`int`):
The id of the token to force as the last generated token when :obj:`max_length` is reached.
"""
def __init__(self, max_length: int, eos_token_id: int):
self.max_length = max_length
self.eos_token_id = eos_token_id
def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor) -> torch.FloatTensor:
cur_len = input_ids.shape[-1]
if cur_len == self.max_length - 1:
num_tokens = scores.shape[1]
scores[:, [i for i in range(num_tokens) if i != self.eos_token_id]] = -float("inf")
scores[:, self.eos_token_id] = 0
return scores
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