"""Chain for chatting with a vector database.""" from __future__ import annotations import inspect import warnings from abc import abstractmethod from collections.abc import Callable from pathlib import Path from typing import Any from langchain_core._api import deprecated from langchain_core.callbacks import ( AsyncCallbackManagerForChainRun, CallbackManagerForChainRun, Callbacks, ) from langchain_core.documents import Document from langchain_core.language_models import BaseLanguageModel from langchain_core.messages import BaseMessage from langchain_core.prompts import BasePromptTemplate from langchain_core.retrievers import BaseRetriever from langchain_core.runnables import RunnableConfig from langchain_core.vectorstores import VectorStore from pydantic import BaseModel, ConfigDict, Field, model_validator from typing_extensions import override from langchain_classic.chains.base import Chain from langchain_classic.chains.combine_documents.base import BaseCombineDocumentsChain from langchain_classic.chains.combine_documents.stuff import StuffDocumentsChain from langchain_classic.chains.conversational_retrieval.prompts import ( CONDENSE_QUESTION_PROMPT, ) from langchain_classic.chains.llm import LLMChain from langchain_classic.chains.question_answering import load_qa_chain # Depending on the memory type and configuration, the chat history format may differ. # This needs to be consolidated. CHAT_TURN_TYPE = tuple[str, str] | BaseMessage _ROLE_MAP = {"human": "Human: ", "ai": "Assistant: "} def _get_chat_history(chat_history: list[CHAT_TURN_TYPE]) -> str: buffer = "" for dialogue_turn in chat_history: if isinstance(dialogue_turn, BaseMessage): if len(dialogue_turn.content) > 0: role_prefix = _ROLE_MAP.get( dialogue_turn.type, f"{dialogue_turn.type}: ", ) buffer += f"\n{role_prefix}{dialogue_turn.content}" elif isinstance(dialogue_turn, tuple): human = "Human: " + dialogue_turn[0] ai = "Assistant: " + dialogue_turn[1] buffer += f"\n{human}\n{ai}" else: msg = ( # type: ignore[unreachable] f"Unsupported chat history format: {type(dialogue_turn)}." f" Full chat history: {chat_history} " ) raise ValueError(msg) # noqa: TRY004 return buffer class InputType(BaseModel): """Input type for ConversationalRetrievalChain.""" question: str """The question to answer.""" chat_history: list[CHAT_TURN_TYPE] = Field(default_factory=list) """The chat history to use for retrieval.""" class BaseConversationalRetrievalChain(Chain): """Chain for chatting with an index.""" combine_docs_chain: BaseCombineDocumentsChain """The chain used to combine any retrieved documents.""" question_generator: LLMChain """The chain used to generate a new question for the sake of retrieval. This chain will take in the current question (with variable `question`) and any chat history (with variable `chat_history`) and will produce a new standalone question to be used later on.""" output_key: str = "answer" """The output key to return the final answer of this chain in.""" rephrase_question: bool = True """Whether or not to pass the new generated question to the combine_docs_chain. If `True`, will pass the new generated question along. If `False`, will only use the new generated question for retrieval and pass the original question along to the combine_docs_chain.""" return_source_documents: bool = False """Return the retrieved source documents as part of the final result.""" return_generated_question: bool = False """Return the generated question as part of the final result.""" get_chat_history: Callable[[list[CHAT_TURN_TYPE]], str] | None = None """An optional function to get a string of the chat history. If `None` is provided, will use a default.""" response_if_no_docs_found: str | None = None """If specified, the chain will return a fixed response if no docs are found for the question. """ model_config = ConfigDict( populate_by_name=True, arbitrary_types_allowed=True, extra="forbid", ) @property def input_keys(self) -> list[str]: """Input keys.""" return ["question", "chat_history"] @override def get_input_schema( self, config: RunnableConfig | None = None, ) -> type[BaseModel]: return InputType @property def output_keys(self) -> list[str]: """Return the output keys.""" _output_keys = [self.output_key] if self.return_source_documents: _output_keys = [*_output_keys, "source_documents"] if self.return_generated_question: _output_keys = [*_output_keys, "generated_question"] return _output_keys @abstractmethod def _get_docs( self, question: str, inputs: dict[str, Any], *, run_manager: CallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" def _call( self, inputs: dict[str, Any], run_manager: CallbackManagerForChainRun | None = None, ) -> dict[str, Any]: _run_manager = run_manager or CallbackManagerForChainRun.get_noop_manager() 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: callbacks = _run_manager.get_child() new_question = self.question_generator.run( question=question, chat_history=chat_history_str, callbacks=callbacks, ) else: new_question = question accepts_run_manager = ( "run_manager" in inspect.signature(self._get_docs).parameters ) if accepts_run_manager: docs = self._get_docs(new_question, inputs, run_manager=_run_manager) else: docs = self._get_docs(new_question, inputs) # type: ignore[call-arg] output: dict[str, Any] = {} if self.response_if_no_docs_found is not None and len(docs) == 0: output[self.output_key] = self.response_if_no_docs_found else: new_inputs = inputs.copy() if self.rephrase_question: new_inputs["question"] = new_question new_inputs["chat_history"] = chat_history_str answer = self.combine_docs_chain.run( input_documents=docs, callbacks=_run_manager.get_child(), **new_inputs, ) output[self.output_key] = answer if self.return_source_documents: output["source_documents"] = docs if self.return_generated_question: output["generated_question"] = new_question return output @abstractmethod async def _aget_docs( self, question: str, inputs: dict[str, Any], *, run_manager: AsyncCallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" async def _acall( self, inputs: dict[str, Any], run_manager: AsyncCallbackManagerForChainRun | None = None, ) -> dict[str, Any]: _run_manager = run_manager or AsyncCallbackManagerForChainRun.get_noop_manager() 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: callbacks = _run_manager.get_child() new_question = await self.question_generator.arun( question=question, chat_history=chat_history_str, callbacks=callbacks, ) else: new_question = question accepts_run_manager = ( "run_manager" in inspect.signature(self._aget_docs).parameters ) if accepts_run_manager: docs = await self._aget_docs(new_question, inputs, run_manager=_run_manager) else: docs = await self._aget_docs(new_question, inputs) # type: ignore[call-arg] output: dict[str, Any] = {} if self.response_if_no_docs_found is not None and len(docs) == 0: output[self.output_key] = self.response_if_no_docs_found else: new_inputs = inputs.copy() if self.rephrase_question: new_inputs["question"] = new_question new_inputs["chat_history"] = chat_history_str answer = await self.combine_docs_chain.arun( input_documents=docs, callbacks=_run_manager.get_child(), **new_inputs, ) output[self.output_key] = answer if self.return_source_documents: output["source_documents"] = docs if self.return_generated_question: output["generated_question"] = new_question return output @override def save(self, file_path: Path | str) -> None: if self.get_chat_history: msg = "Chain not saveable when `get_chat_history` is not None." raise ValueError(msg) super().save(file_path) @deprecated( since="0.1.17", alternative=( "create_history_aware_retriever together with create_retrieval_chain " "(see example in docstring)" ), removal="1.0", ) class ConversationalRetrievalChain(BaseConversationalRetrievalChain): r"""Chain for having a conversation based on retrieved documents. This class is deprecated. See below for an example implementation using `create_retrieval_chain`. Additional walkthroughs can be found at https://python.langchain.com/docs/use_cases/question_answering/chat_history ```python from langchain_classic.chains import ( create_history_aware_retriever, create_retrieval_chain, ) from langchain_classic.chains.combine_documents import ( create_stuff_documents_chain, ) from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder from langchain_openai import ChatOpenAI retriever = ... # Your retriever model = ChatOpenAI() # Contextualize question contextualize_q_system_prompt = ( "Given a chat history and the latest user question " "which might reference context in the chat history, " "formulate a standalone question which can be understood " "without the chat history. Do NOT answer the question, just " "reformulate it if needed and otherwise return it as is." ) contextualize_q_prompt = ChatPromptTemplate.from_messages( [ ("system", contextualize_q_system_prompt), MessagesPlaceholder("chat_history"), ("human", "{input}"), ] ) history_aware_retriever = create_history_aware_retriever( model, retriever, contextualize_q_prompt ) # Answer question qa_system_prompt = ( "You are an assistant for question-answering tasks. Use " "the following pieces of retrieved context to answer the " "question. If you don't know the answer, just say that you " "don't know. Use three sentences maximum and keep the answer " "concise." "\n\n" "{context}" ) qa_prompt = ChatPromptTemplate.from_messages( [ ("system", qa_system_prompt), MessagesPlaceholder("chat_history"), ("human", "{input}"), ] ) # Below we use create_stuff_documents_chain to feed all retrieved context # into the LLM. Note that we can also use StuffDocumentsChain and other # instances of BaseCombineDocumentsChain. question_answer_chain = create_stuff_documents_chain(model, qa_prompt) rag_chain = create_retrieval_chain(history_aware_retriever, question_answer_chain) # Usage: chat_history = [] # Collect chat history here (a sequence of messages) rag_chain.invoke({"input": query, "chat_history": chat_history}) ``` This chain takes in chat history (a list of messages) and new questions, and then returns an answer to that question. The algorithm for this chain consists of three parts: 1. Use the chat history and the new question to create a "standalone question". This is done so that this question can be passed into the retrieval step to fetch relevant documents. If only the new question was passed in, then relevant context may be lacking. If the whole conversation was passed into retrieval, there may be unnecessary information there that would distract from retrieval. 2. This new question is passed to the retriever and relevant documents are returned. 3. The retrieved documents are passed to an LLM along with either the new question (default behavior) or the original question and chat history to generate a final response. Example: ```python from langchain_classic.chains import ( StuffDocumentsChain, LLMChain, ConversationalRetrievalChain, ) from langchain_core.prompts import PromptTemplate from langchain_openai import OpenAI combine_docs_chain = StuffDocumentsChain(...) vectorstore = ... retriever = vectorstore.as_retriever() # This controls how the standalone question is generated. # Should take `chat_history` and `question` as input variables. template = ( "Combine the chat history and follow up question into " "a standalone question. Chat History: {chat_history}" "Follow up question: {question}" ) prompt = PromptTemplate.from_template(template) model = OpenAI() question_generator_chain = LLMChain(llm=model, prompt=prompt) chain = ConversationalRetrievalChain( combine_docs_chain=combine_docs_chain, retriever=retriever, question_generator=question_generator_chain, ) ``` """ retriever: BaseRetriever """Retriever to use to fetch documents.""" max_tokens_limit: int | None = None """If set, enforces that the documents returned are less than this limit. This is only enforced if `combine_docs_chain` is of type StuffDocumentsChain. """ def _reduce_tokens_below_limit(self, docs: list[Document]) -> list[Document]: num_docs = len(docs) if self.max_tokens_limit and isinstance( self.combine_docs_chain, StuffDocumentsChain, ): tokens = [ self.combine_docs_chain.llm_chain._get_num_tokens(doc.page_content) # noqa: SLF001 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] @override def _get_docs( self, question: str, inputs: dict[str, Any], *, run_manager: CallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" docs = self.retriever.invoke( question, config={"callbacks": run_manager.get_child()}, ) return self._reduce_tokens_below_limit(docs) @override async def _aget_docs( self, question: str, inputs: dict[str, Any], *, run_manager: AsyncCallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" docs = await self.retriever.ainvoke( question, config={"callbacks": run_manager.get_child()}, ) return self._reduce_tokens_below_limit(docs) @classmethod def from_llm( cls, llm: BaseLanguageModel, retriever: BaseRetriever, condense_question_prompt: BasePromptTemplate = CONDENSE_QUESTION_PROMPT, chain_type: str = "stuff", verbose: bool = False, # noqa: FBT001,FBT002 condense_question_llm: BaseLanguageModel | None = None, combine_docs_chain_kwargs: dict | None = None, callbacks: Callbacks = None, **kwargs: Any, ) -> BaseConversationalRetrievalChain: """Convenience method to load chain from LLM and retriever. This provides some logic to create the `question_generator` chain as well as the combine_docs_chain. Args: llm: The default language model to use at every part of this chain (eg in both the question generation and the answering) retriever: The retriever to use to fetch relevant documents from. condense_question_prompt: The prompt to use to condense the chat history and new question into a standalone question. chain_type: The chain type to use to create the combine_docs_chain, will be sent to `load_qa_chain`. verbose: Verbosity flag for logging to stdout. condense_question_llm: The language model to use for condensing the chat history and new question into a standalone question. If none is provided, will default to `llm`. combine_docs_chain_kwargs: Parameters to pass as kwargs to `load_qa_chain` when constructing the combine_docs_chain. callbacks: Callbacks to pass to all subchains. kwargs: Additional parameters to pass when initializing ConversationalRetrievalChain """ combine_docs_chain_kwargs = combine_docs_chain_kwargs or {} doc_chain = load_qa_chain( llm, chain_type=chain_type, verbose=verbose, callbacks=callbacks, **combine_docs_chain_kwargs, ) _llm = condense_question_llm or llm condense_question_chain = LLMChain( llm=_llm, prompt=condense_question_prompt, verbose=verbose, callbacks=callbacks, ) return cls( retriever=retriever, combine_docs_chain=doc_chain, question_generator=condense_question_chain, callbacks=callbacks, **kwargs, ) class ChatVectorDBChain(BaseConversationalRetrievalChain): """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" @model_validator(mode="before") @classmethod def _raise_deprecation(cls, values: dict) -> Any: warnings.warn( "`ChatVectorDBChain` is deprecated - " "please use `from langchain_classic.chains import " "ConversationalRetrievalChain`", stacklevel=4, ) return values @override def _get_docs( self, question: str, inputs: dict[str, Any], *, run_manager: CallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" 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, ) async def _aget_docs( self, question: str, inputs: dict[str, Any], *, run_manager: AsyncCallbackManagerForChainRun, ) -> list[Document]: """Get docs.""" msg = "ChatVectorDBChain does not support async" raise NotImplementedError(msg) @classmethod def from_llm( cls, llm: BaseLanguageModel, vectorstore: VectorStore, condense_question_prompt: BasePromptTemplate = CONDENSE_QUESTION_PROMPT, chain_type: str = "stuff", combine_docs_chain_kwargs: dict | None = None, callbacks: Callbacks = None, **kwargs: Any, ) -> BaseConversationalRetrievalChain: """Load chain from LLM.""" combine_docs_chain_kwargs = combine_docs_chain_kwargs or {} doc_chain = load_qa_chain( llm, chain_type=chain_type, callbacks=callbacks, **combine_docs_chain_kwargs, ) condense_question_chain = LLMChain( llm=llm, prompt=condense_question_prompt, callbacks=callbacks, ) return cls( vectorstore=vectorstore, combine_docs_chain=doc_chain, question_generator=condense_question_chain, callbacks=callbacks, **kwargs, )