"""Sampling parameters for text generation."""
import copy
from enum import IntEnum
from functools import cached_property
from typing import Any, Callable, Dict, List, Optional, Union
import torch
from pydantic import Field
from typing_extensions import Annotated
_SAMPLING_EPS = 1e-5
class SamplingType(IntEnum):
GREEDY = 0
RANDOM = 1
RANDOM_SEED = 2
BEAM = 3
LogitsProcessor = Callable[[List[int], torch.Tensor], torch.Tensor]
"""LogitsProcessor is a function that takes a list of previously generated
tokens and a tensor of the logits for the next token, and returns a modified
tensor of logits to sample from."""
[docs]class SamplingParams:
"""Sampling parameters for text generation.
Overall, we follow the sampling parameters from the OpenAI text completion
API (https://platform.openai.com/docs/api-reference/completions/create).
In addition, we support beam search, which is not supported by OpenAI.
Args:
n: Number of output sequences to return for the given prompt.
best_of: Number of output sequences that are generated from the prompt.
From these `best_of` sequences, the top `n` sequences are returned.
`best_of` must be greater than or equal to `n`. This is treated as
the beam width when `use_beam_search` is True. By default, `best_of`
is set to `n`.
presence_penalty: Float that penalizes new tokens based on whether they
appear in the generated text so far. Values > 0 encourage the model
to use new tokens, while values < 0 encourage the model to repeat
tokens.
frequency_penalty: Float that penalizes new tokens based on their
frequency in the generated text so far. Values > 0 encourage the
model to use new tokens, while values < 0 encourage the model to
repeat tokens.
repetition_penalty: Float that penalizes new tokens based on whether
they appear in the prompt and the generated text so far. Values > 1
encourage the model to use new tokens, while values < 1 encourage
the model to repeat tokens.
temperature: Float that controls the randomness of the sampling. Lower
values make the model more deterministic, while higher values make
the model more random. Zero means greedy sampling.
top_p: Float that controls the cumulative probability of the top tokens
to consider. Must be in (0, 1]. Set to 1 to consider all tokens.
top_k: Integer that controls the number of top tokens to consider. Set
to -1 to consider all tokens.
min_p: Float that represents the minimum probability for a token to be
considered, relative to the probability of the most likely token.
Must be in [0, 1]. Set to 0 to disable this.
seed: Random seed to use for the generation.
use_beam_search: Whether to use beam search instead of sampling.
length_penalty: Float that penalizes sequences based on their length.
Used in beam search.
early_stopping: Controls the stopping condition for beam search. It
accepts the following values: `True`, where the generation stops as
soon as there are `best_of` complete candidates; `False`, where an
heuristic is applied and the generation stops when is it very
unlikely to find better candidates; `"never"`, where the beam search
procedure only stops when there cannot be better candidates
(canonical beam search algorithm).
stop: List of strings that stop the generation when they are generated.
The returned output will not contain the stop strings.
stop_token_ids: List of tokens that stop the generation when they are
generated. The returned output will contain the stop tokens unless
the stop tokens are special tokens.
include_stop_str_in_output: Whether to include the stop strings in
output text. Defaults to False.
ignore_eos: Whether to ignore the EOS token and continue generating
tokens after the EOS token is generated.
max_tokens: Maximum number of tokens to generate per output sequence.
min_tokens: Minimum number of tokens to generate per output sequence
before EOS or stop_token_ids can be generated
logprobs: Number of log probabilities to return per output token.
Note that the implementation follows the OpenAI API: The return
result includes the log probabilities on the `logprobs` most likely
tokens, as well the chosen tokens. The API will always return the
log probability of the sampled token, so there may be up to
`logprobs+1` elements in the response.
prompt_logprobs: Number of log probabilities to return per prompt token.
detokenize: Whether to detokenize the output. Defaults to True.
skip_special_tokens: Whether to skip special tokens in the output.
spaces_between_special_tokens: Whether to add spaces between special
tokens in the output. Defaults to True.
logits_processors: List of functions that modify logits based on
previously generated tokens.
truncate_prompt_tokens: If set to an integer k, will use only the last k
tokens from the prompt (i.e., left truncation). Defaults to None
(i.e., no truncation).
"""
def __init__(
self,
n: int = 1,
best_of: Optional[int] = None,
presence_penalty: float = 0.0,
frequency_penalty: float = 0.0,
repetition_penalty: float = 1.0,
temperature: float = 1.0,
top_p: float = 1.0,
top_k: int = -1,
min_p: float = 0.0,
seed: Optional[int] = None,
use_beam_search: bool = False,
length_penalty: float = 1.0,
early_stopping: Union[bool, str] = False,
stop: Optional[Union[str, List[str]]] = None,
stop_token_ids: Optional[List[int]] = None,
include_stop_str_in_output: bool = False,
ignore_eos: bool = False,
max_tokens: Optional[int] = 16,
min_tokens: int = 0,
logprobs: Optional[int] = None,
prompt_logprobs: Optional[int] = None,
detokenize: bool = True,
skip_special_tokens: bool = True,
spaces_between_special_tokens: bool = True,
logits_processors: Optional[List[LogitsProcessor]] = None,
truncate_prompt_tokens: Optional[Annotated[int, Field(ge=1)]] = None,
) -> None:
self.n = n
self.best_of = best_of if best_of is not None else n
self.presence_penalty = presence_penalty
self.frequency_penalty = frequency_penalty
self.repetition_penalty = repetition_penalty
self.temperature = temperature
self.top_p = top_p
self.top_k = top_k
self.min_p = min_p
if seed == -1:
self.seed = None
else:
self.seed = seed
self.use_beam_search = use_beam_search
self.length_penalty = length_penalty
self.early_stopping = early_stopping
if stop is None:
self.stop = []
elif isinstance(stop, str):
self.stop = [stop]
else:
self.stop = list(stop)
if stop_token_ids is None:
self.stop_token_ids = []
else:
self.stop_token_ids = list(stop_token_ids)
self.ignore_eos = ignore_eos
self.max_tokens = max_tokens
self.min_tokens = min_tokens
self.logprobs = logprobs
self.prompt_logprobs = prompt_logprobs
# NOTE: This parameter is only exposed at the engine level for now.
# It is not exposed in the OpenAI API server, as the OpenAI API does
# not support returning only a list of token IDs.
self.detokenize = detokenize
self.skip_special_tokens = skip_special_tokens
self.spaces_between_special_tokens = spaces_between_special_tokens
self.logits_processors = logits_processors
self.include_stop_str_in_output = include_stop_str_in_output
self.truncate_prompt_tokens = truncate_prompt_tokens
# Number of characters to hold back for stop string evaluation
# until sequence is finished.
if self.stop and not include_stop_str_in_output:
self.output_text_buffer_length = max(len(s) for s in self.stop) - 1
else:
self.output_text_buffer_length = 0
self._verify_args()
if self.use_beam_search:
self._verify_beam_search()
else:
self._verify_non_beam_search()
if self.temperature < _SAMPLING_EPS:
# Zero temperature means greedy sampling.
self.top_p = 1.0
self.top_k = -1
self.min_p = 0.0
self._verify_greedy_sampling()
# eos_token_id is added to this by the engine
self.all_stop_token_ids = set(self.stop_token_ids)
def _verify_args(self) -> None:
if self.n < 1:
raise ValueError(f"n must be at least 1, got {self.n}.")
if self.best_of < self.n:
raise ValueError(f"best_of must be greater than or equal to n, "
f"got n={self.n} and best_of={self.best_of}.")
if not -2.0 <= self.presence_penalty <= 2.0:
raise ValueError("presence_penalty must be in [-2, 2], got "
f"{self.presence_penalty}.")
if not -2.0 <= self.frequency_penalty <= 2.0:
raise ValueError("frequency_penalty must be in [-2, 2], got "
f"{self.frequency_penalty}.")
if not 0.0 < self.repetition_penalty <= 2.0:
raise ValueError("repetition_penalty must be in (0, 2], got "
f"{self.repetition_penalty}.")
if self.temperature < 0.0:
raise ValueError(
f"temperature must be non-negative, got {self.temperature}.")
if not 0.0 < self.top_p <= 1.0:
raise ValueError(f"top_p must be in (0, 1], got {self.top_p}.")
if self.top_k < -1 or self.top_k == 0:
raise ValueError(f"top_k must be -1 (disable), or at least 1, "
f"got {self.top_k}.")
if not 0.0 <= self.min_p <= 1.0:
raise ValueError("min_p must be in [0, 1], got "
f"{self.min_p}.")
if self.max_tokens is not None and self.max_tokens < 1:
raise ValueError(
f"max_tokens must be at least 1, got {self.max_tokens}.")
if self.min_tokens < 0:
raise ValueError(f"min_tokens must be greater than or equal to 0, "
f"got {self.min_tokens}.")
if self.max_tokens is not None and self.min_tokens > self.max_tokens:
raise ValueError(
f"min_tokens must be less than or equal to "
f"max_tokens={self.max_tokens}, got {self.min_tokens}.")
if self.logprobs is not None and self.logprobs < 0:
raise ValueError(
f"logprobs must be non-negative, got {self.logprobs}.")
if self.prompt_logprobs is not None and self.prompt_logprobs < 0:
raise ValueError(f"prompt_logprobs must be non-negative, got "
f"{self.prompt_logprobs}.")
if (self.truncate_prompt_tokens is not None
and self.truncate_prompt_tokens < 1):
raise ValueError(f"truncate_prompt_tokens must be >= 1, "
f"got {self.truncate_prompt_tokens}")
if any(not stop_str for stop_str in self.stop):
raise ValueError("stop cannot contain an empty string.")
if self.stop and not self.detokenize:
raise ValueError(
"stop strings are only supported when detokenize is True. "
"Set detokenize=True to use stop.")
def _verify_beam_search(self) -> None:
if self.best_of == 1:
raise ValueError("best_of must be greater than 1 when using beam "
f"search. Got {self.best_of}.")
if self.temperature > _SAMPLING_EPS:
raise ValueError("temperature must be 0 when using beam search.")
if self.top_p < 1.0 - _SAMPLING_EPS:
raise ValueError("top_p must be 1 when using beam search.")
if self.top_k != -1:
raise ValueError("top_k must be -1 when using beam search.")
if self.early_stopping not in [True, False, "never"]:
raise ValueError(
f"early_stopping must be True, False, or 'never', "
f"got {self.early_stopping}.")
def _verify_non_beam_search(self) -> None:
if self.early_stopping is not False:
raise ValueError("early_stopping is not effective and must be "
"False when not using beam search.")
if (self.length_penalty < 1.0 - _SAMPLING_EPS
or self.length_penalty > 1.0 + _SAMPLING_EPS):
raise ValueError(
"length_penalty is not effective and must be the "
"default value of 1.0 when not using beam search.")
def _verify_greedy_sampling(self) -> None:
if self.best_of > 1:
raise ValueError("best_of must be 1 when using greedy sampling."
f"Got {self.best_of}.")
[docs] def update_from_generation_config(
self, generation_config: Dict[str, Any]) -> None:
"""Update if there are non-default values from generation_config"""
# Update eos_token_id for generation
if (not self.ignore_eos) and (eos_ids :=
generation_config.get("eos_token_id")):
# it can be either int or list of int
if isinstance(eos_ids, int):
eos_ids = [eos_ids]
original_stop_token_ids = set(self.stop_token_ids)
original_stop_token_ids.update(eos_ids)
self.stop_token_ids = list(original_stop_token_ids)
@cached_property
def sampling_type(self) -> SamplingType:
if self.use_beam_search:
return SamplingType.BEAM
if self.temperature < _SAMPLING_EPS:
return SamplingType.GREEDY
if self.seed is not None:
return SamplingType.RANDOM_SEED
return SamplingType.RANDOM
[docs] def clone(self) -> "SamplingParams":
"""Deep copy excluding LogitsProcessor objects.
LogitsProcessor objects are excluded because they may contain an
arbitrary, nontrivial amount of data.
See https://github.com/vllm-project/vllm/issues/3087
"""
logit_processor_refs = None if self.logits_processors is None else {
id(lp): lp
for lp in self.logits_processors
}
return copy.deepcopy(self, memo=logit_processor_refs)
def __repr__(self) -> str:
return (
f"SamplingParams(n={self.n}, "
f"best_of={self.best_of}, "
f"presence_penalty={self.presence_penalty}, "
f"frequency_penalty={self.frequency_penalty}, "
f"repetition_penalty={self.repetition_penalty}, "
f"temperature={self.temperature}, "
f"top_p={self.top_p}, "
f"top_k={self.top_k}, "
f"min_p={self.min_p}, "
f"seed={self.seed}, "
f"use_beam_search={self.use_beam_search}, "
f"length_penalty={self.length_penalty}, "
f"early_stopping={self.early_stopping}, "
f"stop={self.stop}, "
f"stop_token_ids={self.stop_token_ids}, "
f"include_stop_str_in_output={self.include_stop_str_in_output}, "
f"ignore_eos={self.ignore_eos}, "
f"max_tokens={self.max_tokens}, "
f"min_tokens={self.min_tokens}, "
f"logprobs={self.logprobs}, "
f"prompt_logprobs={self.prompt_logprobs}, "
f"skip_special_tokens={self.skip_special_tokens}, "
"spaces_between_special_tokens="
f"{self.spaces_between_special_tokens}, "
f"truncate_prompt_tokens={self.truncate_prompt_tokens})")
