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"""Question-answering with sources over a vector database."""
from typing import Any, Dict, List
from pydantic import BaseModel, Field
from langchain.chains.combine_documents.stuff import StuffDocumentsChain
from langchain.chains.qa_with_sources.base import BaseQAWithSourcesChain
from langchain.docstore.document import Document
from langchain.vectorstores.base import VectorStore
class VectorDBQAWithSourcesChain(BaseQAWithSourcesChain, BaseModel):
"""Question-answering with sources over a vector database."""
vectorstore: VectorStore = Field(exclude=True)
"""Vector Database to connect to."""
k: int = 4
"""Number of results to return from store"""
reduce_k_below_max_tokens: bool = False
"""Reduce the number of results to return from store based on tokens limit"""
max_tokens_limit: int = 3375
"""Restrict the docs to return from store based on tokens,
enforced only for StuffDocumentChain and if reduce_k_below_max_tokens is to true"""
search_kwargs: Dict[str, Any] = Field(default_factory=dict)
"""Extra search args."""
def _reduce_tokens_below_limit(self, docs: List[Document]) -> List[Document]:
num_docs = len(docs)
if self.reduce_k_below_max_tokens and isinstance(
self.combine_documents_chain, StuffDocumentsChain
):
tokens = [
self.combine_documents_chain.llm_chain.llm.get_num_tokens(
doc.page_content
)
for doc in docs
]
token_count = sum(tokens[:num_docs])
while token_count > self.max_tokens_limit:
num_docs -= 1
token_count -= tokens[num_docs]
return docs[:num_docs]
def _get_docs(self, inputs: Dict[str, Any]) -> List[Document]:
question = inputs[self.question_key]
docs = self.vectorstore.similarity_search(
question, k=self.k, **self.search_kwargs
)
return self._reduce_tokens_below_limit(docs)
@property
def _chain_type(self) -> str:
return "vector_db_qa_with_sources_chain"
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