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import re
import numpy as np
from transformers import Pipeline, PreTrainedTokenizer
INSTRUCTION_KEY = "### Instruction:"
RESPONSE_KEY = "### Response:"
END_KEY = "### End"
INTRO_BLURB = (
"Below is an instruction that describes a task, along with any additional context. Write a response that appropriately completes the request."
)
# This is the prompt that is used for generating responses using an already trained model. It ends with the response
# key, where the job of the model is to provide the completion that follows it (i.e. the response itself).
PROMPT_FOR_GENERATION_FORMAT = """{intro}
{instruction_key}
{instruction}
{response_key}
""".format(
intro=INTRO_BLURB,
instruction_key=INSTRUCTION_KEY,
instruction="{instruction}",
response_key=RESPONSE_KEY,
)
def get_special_token_id(tokenizer: PreTrainedTokenizer, key: str) -> int:
"""Gets the token ID for a given string that has been added to the tokenizer as a special token.
When training, we configure the tokenizer so that the sequences like "### Instruction:" and "### End" are
treated specially and converted to a single, new token. This retrieves the token ID each of these keys map to.
Args:
tokenizer (PreTrainedTokenizer): the tokenizer
key (str): the key to convert to a single token
Raises:
RuntimeError: if more than one ID was generated
Returns:
int: the token ID for the given key
"""
token_ids = tokenizer.encode(key)
if len(token_ids) > 1:
raise ValueError(f"Expected only a single token for '{key}' but found {token_ids}")
return token_ids[0]
class InstructionTextGenerationPipeline(Pipeline):
def __init__(
self, *args, do_sample: bool = True, max_new_tokens: int = 256, top_p: float = 0.92, top_k: int = 0, **kwargs
):
super().__init__(*args, do_sample=do_sample, max_new_tokens=max_new_tokens, top_p=top_p, top_k=top_k, **kwargs)
def _sanitize_parameters(self, return_instruction_text=False, **generate_kwargs):
preprocess_params = {}
# newer versions of the tokenizer configure the response key as a special token. newer versions still may
# append a newline to yield a single token. find whatever token is configured for the response key.
tokenizer_response_key = next(
(token for token in self.tokenizer.additional_special_tokens if token.startswith(RESPONSE_KEY)), None
)
response_key_token_id = None
end_key_token_id = None
if tokenizer_response_key:
try:
response_key_token_id = get_special_token_id(self.tokenizer, tokenizer_response_key)
end_key_token_id = get_special_token_id(self.tokenizer, END_KEY)
# Ensure generation stops once it generates "### End"
generate_kwargs["eos_token_id"] = end_key_token_id
except ValueError:
pass
forward_params = generate_kwargs
postprocess_params = {
"response_key_token_id": response_key_token_id,
"end_key_token_id": end_key_token_id,
"return_instruction_text": return_instruction_text,
}
return preprocess_params, forward_params, postprocess_params
def preprocess(self, instruction_text, **generate_kwargs):
prompt_text = PROMPT_FOR_GENERATION_FORMAT.format(instruction=instruction_text)
inputs = self.tokenizer(
prompt_text,
return_tensors="pt",
)
inputs["prompt_text"] = prompt_text
inputs["instruction_text"] = instruction_text
return inputs
def _forward(self, model_inputs, **generate_kwargs):
input_ids = model_inputs["input_ids"]
attention_mask = model_inputs.get("attention_mask", None)
generated_sequence = self.model.generate(
input_ids=input_ids.to(self.model.device),
attention_mask=attention_mask,
pad_token_id=self.tokenizer.pad_token_id,
**generate_kwargs,
)[0].cpu()
instruction_text = model_inputs.pop("instruction_text")
return {"generated_sequence": generated_sequence, "input_ids": input_ids, "instruction_text": instruction_text}
def postprocess(self, model_outputs, response_key_token_id, end_key_token_id, return_instruction_text):
sequence = model_outputs["generated_sequence"]
instruction_text = model_outputs["instruction_text"]
# The response will be set to this variable if we can identify it.
decoded = None
# If we have token IDs for the response and end, then we can find the tokens and only decode between them.
if response_key_token_id and end_key_token_id:
# Find where "### Response:" is first found in the generated tokens. Considering this is part of the
# prompt, we should definitely find it. We will return the tokens found after this token.
response_pos = None
response_positions = np.where(sequence == response_key_token_id)[0]
if len(response_positions) == 0:
pass
else:
response_pos = response_positions[0]
if response_pos:
# Next find where "### End" is located. The model has been trained to end its responses with this
# sequence (or actually, the token ID it maps to, since it is a special token). We may not find
# this token, as the response could be truncated. If we don't find it then just return everything
# to the end. Note that even though we set eos_token_id, we still see the this token at the end.
end_pos = None
end_positions = np.where(sequence == end_key_token_id)[0]
if len(end_positions) > 0:
end_pos = end_positions[0]
decoded = self.tokenizer.decode(sequence[response_pos + 1 : end_pos]).strip()
else:
# Otherwise we'll decode everything and use a regex to find the response and end.
fully_decoded = self.tokenizer.decode(sequence)
# The response appears after "### Response:". The model has been trained to append "### End" at the
# end.
m = re.search(r"#+\s*Response:\s*(.+?)#+\s*End", fully_decoded, flags=re.DOTALL)
if m:
decoded = m.group(1).strip()
else:
# The model might not generate the "### End" sequence before reaching the max tokens. In this case,
# return everything after "### Response:".
m = re.search(r"#+\s*Response:\s*(.+)", fully_decoded, flags=re.DOTALL)
if m:
decoded = m.group(1).strip()
if return_instruction_text:
return {"instruction_text": instruction_text, "generated_text": decoded}
return decoded
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