62 lines
1.7 KiB
Python
62 lines
1.7 KiB
Python
from dataclasses import dataclass
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from typing import List, Optional
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@dataclass
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class BeamSearchSequence:
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"""A sequence for beam search.
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It keeps track of the tokens and the log probability of the sequence.
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The text field is optional and will only be filled when the sequence is
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about to be returned to the user.
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"""
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# The tokens includes the prompt.
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tokens: List[int]
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cum_logprob: float = 0.0
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text: Optional[str] = None
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@dataclass
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class BeamSearchOutput:
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"""The output of beam search.
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It contains the list of the best beam search sequences.
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The length of the list is equal to the beam width.
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"""
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sequences: List[BeamSearchSequence]
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class BeamSearchInstance:
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def __init__(self, prompt_tokens: List[int]):
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self.beams: List[BeamSearchSequence] = [
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BeamSearchSequence(tokens=prompt_tokens)
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]
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self.completed: List[BeamSearchSequence] = []
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def get_beam_search_score(
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tokens: List[int],
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cumulative_logprob: float,
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eos_token_id: int,
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length_penalty: float = 1.0,
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) -> float:
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"""Calculate the beam search score with length penalty.
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Adapted from
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https://github.com/huggingface/transformers/blob/ccb92be23def445f2afdea94c31286f84b89eb5b/src/transformers/generation/beam_search.py#L938
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"""
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seq_len = len(tokens)
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if tokens[-1] == eos_token_id:
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seq_len -= 1
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return cumulative_logprob / (seq_len**length_penalty)
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def create_sort_beams_key_function(eos_token_id: int, length_penalty: float):
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def sort_beams_key(x: BeamSearchSequence) -> float:
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return get_beam_search_score(x.tokens, x.cum_logprob, eos_token_id,
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length_penalty)
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return sort_beams_key
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