langchain/chains/conversational_retrieval/base.py

"""Chain for chatting with a vector database."""
from __future__ import annotations

from abc import abstractmethod
from pathlib import Path
from typing import Any, Callable, Dict, List, Optional, Tuple, Union

from pydantic import BaseModel, Extra, Field

from langchain.chains.base import Chain
from langchain.chains.combine_documents.base import BaseCombineDocumentsChain
from langchain.chains.conversational_retrieval.prompts import CONDENSE_QUESTION_PROMPT
from langchain.chains.llm import LLMChain
from langchain.chains.question_answering import load_qa_chain
from langchain.prompts.base import BasePromptTemplate
from langchain.schema import BaseLanguageModel, BaseRetriever, Document
from langchain.vectorstores.base import VectorStore


def _get_chat_history(chat_history: List[Tuple[str, str]]) -> str:
    buffer = ""
    for human_s, ai_s in chat_history:
        human = "Human: " + human_s
        ai = "Assistant: " + ai_s
        buffer += "\n" + "\n".join([human, ai])
    return buffer


class BaseConversationalRetrievalChain(Chain, BaseModel):
    """Chain for chatting with an index."""

    combine_docs_chain: BaseCombineDocumentsChain
    question_generator: LLMChain
    output_key: str = "answer"
    return_source_documents: bool = False
    get_chat_history: Optional[Callable[[Tuple[str, str]], str]] = None
    """Return the source documents."""

    class Config:
        """Configuration for this pydantic object."""

        extra = Extra.forbid
        arbitrary_types_allowed = True
        allow_population_by_field_name = True

    @property
    def input_keys(self) -> List[str]:
        """Input keys."""
        return ["question", "chat_history"]

    @property
    def output_keys(self) -> List[str]:
        """Return the output keys.

        :meta private:
        """
        _output_keys = [self.output_key]
        if self.return_source_documents:
            _output_keys = _output_keys + ["source_documents"]
        return _output_keys

    @abstractmethod
    def _get_docs(self, question: str, inputs: Dict[str, Any]) -> List[Document]:
        """Get docs."""

    def _call(self, inputs: Dict[str, Any]) -> Dict[str, Any]:
        question = inputs["question"]
        get_chat_history = self.get_chat_history or _get_chat_history
        chat_history_str = get_chat_history(inputs["chat_history"])

        if chat_history_str:
            new_question = self.question_generator.run(
                question=question, chat_history=chat_history_str
            )
        else:
            new_question = question
        docs = self._get_docs(new_question, inputs)
        new_inputs = inputs.copy()
        new_inputs["question"] = new_question
        new_inputs["chat_history"] = chat_history_str
        answer, _ = self.combine_docs_chain.combine_docs(docs, **new_inputs)
        if self.return_source_documents:
            return {self.output_key: answer, "source_documents": docs}
        else:
            return {self.output_key: answer}

    async def _acall(self, inputs: Dict[str, Any]) -> Dict[str, Any]:
        question = inputs["question"]
        get_chat_history = self.get_chat_history or _get_chat_history
        chat_history_str = get_chat_history(inputs["chat_history"])
        if chat_history_str:
            new_question = await self.question_generator.arun(
                question=question, chat_history=chat_history_str
            )
        else:
            new_question = question
        # TODO: This blocks the event loop, but it's not clear how to avoid it.
        docs = self._get_docs(new_question, inputs)
        new_inputs = inputs.copy()
        new_inputs["question"] = new_question
        new_inputs["chat_history"] = chat_history_str
        answer, _ = await self.combine_docs_chain.acombine_docs(docs, **new_inputs)
        if self.return_source_documents:
            return {self.output_key: answer, "source_documents": docs}
        else:
            return {self.output_key: answer}

    def save(self, file_path: Union[Path, str]) -> None:
        if self.get_chat_history:
            raise ValueError("Chain not savable when `get_chat_history` is not None.")
        super().save(file_path)


class ConversationalRetrievalChain(BaseConversationalRetrievalChain, BaseModel):
    """Chain for chatting with an index."""

    retriever: BaseRetriever

    def _get_docs(self, question: str, inputs: Dict[str, Any]) -> List[Document]:
        return self.retriever.get_relevant_texts(question)

    @classmethod
    def from_llm(
        cls,
        llm: BaseLanguageModel,
        retriever: BaseRetriever,
        condense_question_prompt: BasePromptTemplate = CONDENSE_QUESTION_PROMPT,
        qa_prompt: Optional[BasePromptTemplate] = None,
        chain_type: str = "stuff",
        **kwargs: Any,
    ) -> BaseConversationalRetrievalChain:
        """Load chain from LLM."""
        doc_chain = load_qa_chain(
            llm,
            chain_type=chain_type,
            prompt=qa_prompt,
        )
        condense_question_chain = LLMChain(llm=llm, prompt=condense_question_prompt)
        return cls(
            retriever=retriever,
            combine_docs_chain=doc_chain,
            question_generator=condense_question_chain,
            **kwargs,
        )


class ChatVectorDBChain(BaseConversationalRetrievalChain, BaseModel):
    """Chain for chatting with a vector database."""

    vectorstore: VectorStore = Field(alias="vectorstore")
    top_k_docs_for_context: int = 4
    search_kwargs: dict = Field(default_factory=dict)

    @property
    def _chain_type(self) -> str:
        return "chat-vector-db"

    def _get_docs(self, question: str, inputs: Dict[str, Any]) -> List[Document]:
        vectordbkwargs = inputs.get("vectordbkwargs", {})
        full_kwargs = {**self.search_kwargs, **vectordbkwargs}
        return self.vectorstore.similarity_search(
            question, k=self.top_k_docs_for_context, **full_kwargs
        )

    @classmethod
    def from_llm(
        cls,
        llm: BaseLanguageModel,
        vectorstore: VectorStore,
        condense_question_prompt: BasePromptTemplate = CONDENSE_QUESTION_PROMPT,
        qa_prompt: Optional[BasePromptTemplate] = None,
        chain_type: str = "stuff",
        **kwargs: Any,
    ) -> BaseConversationalRetrievalChain:
        """Load chain from LLM."""
        doc_chain = load_qa_chain(
            llm,
            chain_type=chain_type,
            prompt=qa_prompt,
        )
        condense_question_chain = LLMChain(llm=llm, prompt=condense_question_prompt)
        return cls(
            vectorstore=vectorstore,
            combine_docs_chain=doc_chain,
            question_generator=condense_question_chain,
            **kwargs,
        )