BaseQAWithSourcesChain Class — langchain Architecture

Architecture documentation for the BaseQAWithSourcesChain class in base.py from the langchain codebase.

Class python

Entity Profile

Dependency Diagram

graph TD
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54["BaseQAWithSourcesChain"]
  097a4781_5519_0b5d_6244_98c64eadc0d6["Chain"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|extends| 097a4781_5519_0b5d_6244_98c64eadc0d6
  fdc86f9f_85df_84cf_83a4_a9e587fe40ec["base.py"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|defined in| fdc86f9f_85df_84cf_83a4_a9e587fe40ec
  3557b460_a881_8b6e_04c6_e6375e302978["from_llm()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 3557b460_a881_8b6e_04c6_e6375e302978
  4638149d_1d06_b222_a5b6_c92bab187030["from_chain_type()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 4638149d_1d06_b222_a5b6_c92bab187030
  60253345_0524_01a8_20ad_82e3d60555c2["input_keys()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 60253345_0524_01a8_20ad_82e3d60555c2
  41e380be_6c0e_496d_a372_cb481ff4a2ac["output_keys()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 41e380be_6c0e_496d_a372_cb481ff4a2ac
  9c06df47_d1c2_a179_906f_6229e28720f3["validate_naming()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 9c06df47_d1c2_a179_906f_6229e28720f3
  2aa33a84_9121_0a57_1fba_35beb1bb676b["_split_sources()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 2aa33a84_9121_0a57_1fba_35beb1bb676b
  0a571725_c0af_8092_7e91_7f522a43efd1["_get_docs()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 0a571725_c0af_8092_7e91_7f522a43efd1
  80dcc576_05d1_33a1_4182_ba9b68bcd9ce["_call()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 80dcc576_05d1_33a1_4182_ba9b68bcd9ce
  bcc00dbe_47c9_7eb1_2cd3_15702059ce34["_aget_docs()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| bcc00dbe_47c9_7eb1_2cd3_15702059ce34
  62e4e7f4_e493_f37a_5e6c_90b7c0cc140b["_acall()"]
  916d1ca4_2df3_6007_0b8a_5943c3b4bd54 -->|method| 62e4e7f4_e493_f37a_5e6c_90b7c0cc140b

Relationship Graph

Source Code

libs/langchain/langchain_classic/chains/qa_with_sources/base.py lines 46–215

class BaseQAWithSourcesChain(Chain, ABC):
    """Question answering chain with sources over documents."""

    combine_documents_chain: BaseCombineDocumentsChain
    """Chain to use to combine documents."""
    question_key: str = "question"
    input_docs_key: str = "docs"
    answer_key: str = "answer"
    sources_answer_key: str = "sources"
    return_source_documents: bool = False
    """Return the source documents."""

    @classmethod
    def from_llm(
        cls,
        llm: BaseLanguageModel,
        document_prompt: BasePromptTemplate = EXAMPLE_PROMPT,
        question_prompt: BasePromptTemplate = QUESTION_PROMPT,
        combine_prompt: BasePromptTemplate = COMBINE_PROMPT,
        **kwargs: Any,
    ) -> BaseQAWithSourcesChain:
        """Construct the chain from an LLM."""
        llm_question_chain = LLMChain(llm=llm, prompt=question_prompt)
        llm_combine_chain = LLMChain(llm=llm, prompt=combine_prompt)
        combine_results_chain = StuffDocumentsChain(
            llm_chain=llm_combine_chain,
            document_prompt=document_prompt,
            document_variable_name="summaries",
        )
        reduce_documents_chain = ReduceDocumentsChain(
            combine_documents_chain=combine_results_chain,
        )
        combine_documents_chain = MapReduceDocumentsChain(
            llm_chain=llm_question_chain,
            reduce_documents_chain=reduce_documents_chain,
            document_variable_name="context",
        )
        return cls(
            combine_documents_chain=combine_documents_chain,
            **kwargs,
        )

    @classmethod
    def from_chain_type(
        cls,
        llm: BaseLanguageModel,
        chain_type: str = "stuff",
        chain_type_kwargs: dict | None = None,
        **kwargs: Any,
    ) -> BaseQAWithSourcesChain:
        """Load chain from chain type."""
        _chain_kwargs = chain_type_kwargs or {}
        combine_documents_chain = load_qa_with_sources_chain(
            llm,
            chain_type=chain_type,
            **_chain_kwargs,
        )
        return cls(combine_documents_chain=combine_documents_chain, **kwargs)

    model_config = ConfigDict(
        arbitrary_types_allowed=True,
        extra="forbid",
    )

    @property
    def input_keys(self) -> list[str]:
        """Expect input key."""
        return [self.question_key]

    @property
    def output_keys(self) -> list[str]:
        """Return output key."""
        _output_keys = [self.answer_key, self.sources_answer_key]
        if self.return_source_documents:
            _output_keys = [*_output_keys, "source_documents"]
        return _output_keys

    @model_validator(mode="before")
    @classmethod
    def validate_naming(cls, values: dict) -> Any:
        """Fix backwards compatibility in naming."""