Reading LangChain's Summarization Code (1) - Stuff

import os
from langchain.chains.summarize import load_summarize_chain
from langchain_community.document_loaders import WebBaseLoader
from langchain_openai import ChatOpenAI

# Set the API key
with open('.openai') as f:
    os.environ['OPENAI_API_KEY'] = f.read().strip()

# Load the document
loader = WebBaseLoader("https://lilianweng.github.io/posts/2023-06-23-agent/")
docs = loader.load()

# Set up the LLM
llm = ChatOpenAI(temperature=0, model_name="gpt-3.5-turbo-1106")

# Create the summarization chain
chain = load_summarize_chain(llm, chain_type="stuff")

# Execute the summarization
chain.run(docs)

'The article discusses the concept of LLM-powered autonomous agents, focusing on planning, memory, and tool use components. It includes case studies and proof-of-concept examples, as well as challenges and references to related research. The author also provides a citation for the article.'

def load_summarize_chain(
    llm: BaseLanguageModel,
    chain_type: str = "stuff",
    verbose: Optional[bool] = None,
    **kwargs: Any,
) -> BaseCombineDocumentsChain:
    """Load summarizing chain.

    Args:
        llm: Language Model to use in the chain.
        chain_type: Type of document combining chain to use. Should be one of "stuff",
            "map_reduce", and "refine".
        verbose: Whether chains should be run in verbose mode or not. Note that this
            applies to all chains that make up the final chain.

    Returns:
        A chain to use for summarizing.
    """
    loader_mapping: Mapping[str, LoadingCallable] = {
        "stuff": _load_stuff_chain,
        "map_reduce": _load_map_reduce_chain,
        "refine": _load_refine_chain,
    }
    if chain_type not in loader_mapping:
        raise ValueError(
            f"Got unsupported chain type: {chain_type}. "
            f"Should be one of {loader_mapping.keys()}"
        )
    return loader_mapping[chain_type](llm, verbose=verbose, **kwargs)

_load_stuff_chain(llm, verbose=verbose, **kwargs)

def _load_stuff_chain(
    llm: BaseLanguageModel,
    prompt: BasePromptTemplate = stuff_prompt.PROMPT,
    document_variable_name: str = "text",
    verbose: Optional[bool] = None,
    **kwargs: Any,
) -> StuffDocumentsChain:
    llm_chain = LLMChain(llm=llm, prompt=prompt, verbose=verbose)  # type: ignore[arg-type]
    # TODO: document prompt
    return StuffDocumentsChain(
        llm_chain=llm_chain,
        document_variable_name=document_variable_name,
        verbose=verbose,  # type: ignore[arg-type]
        **kwargs,
    )

class StuffDocumentsChain(BaseCombineDocumentsChain):
    """Chain that combines documents by stuffing into context.

    This chain takes a list of documents and first combines them into a single string.
    It does this by formatting each document into a string with the `document_prompt`
    and then joining them together with `document_separator`. It then adds that new
    string to the inputs with the variable name set by `document_variable_name`.
    Those inputs are then passed to the `llm_chain`.

    Example:
        .. code-block:: python

            from langchain.chains import StuffDocumentsChain, LLMChain
            from langchain_core.prompts import PromptTemplate
            from langchain_community.llms import OpenAI

            # This controls how each document will be formatted. Specifically,
            # it will be passed to `format_document` - see that function for more
            # details.
            document_prompt = PromptTemplate(
                input_variables=["page_content"],
                template="{page_content}"
            )
            document_variable_name = "context"
            llm = OpenAI()
            # The prompt here should take as an input variable the
            # `document_variable_name`
            prompt = PromptTemplate.from_template(
                "Summarize this content: {context}"
            )
            llm_chain = LLMChain(llm=llm, prompt=prompt)
            chain = StuffDocumentsChain(
                llm_chain=llm_chain,
                document_prompt=document_prompt,
                document_variable_name=document_variable_name
            )
    """

    llm_chain: LLMChain
    """LLM chain which is called with the formatted document string,
    along with any other inputs."""
    document_prompt: BasePromptTemplate = Field(
        default_factory=lambda: DEFAULT_DOCUMENT_PROMPT
    )
    """Prompt to use to format each document, gets passed to `format_document`."""
    document_variable_name: str
    """The variable name in the llm_chain to put the documents in.
    If only one variable in the llm_chain, this need not be provided."""
    document_separator: str = "\n\n"
    """The string with which to join the formatted documents"""
    ...
    def _get_inputs(self, docs: List[Document], **kwargs: Any) -> dict:
        """Construct inputs from kwargs and docs.

        Format and then join all the documents together into one input with name
        `self.document_variable_name`. Also pluck any additional variables
        from **kwargs.

        Args:
            docs: List of documents to format and then join into single input
            **kwargs: additional inputs to chain, will pluck any other required
                arguments from here.

        Returns:
            dictionary of inputs to LLMChain
        """
        # Format each document according to the prompt
        doc_strings = [format_document(doc, self.document_prompt) for doc in docs]
        # Join the documents together to put them in the prompt.
        inputs = {
            k: v
            for k, v in kwargs.items()
            if k in self.llm_chain.prompt.input_variables
        }
        inputs[self.document_variable_name] = self.document_separator.join(doc_strings)
        return inputs

    ...

    def combine_docs(
        self, docs: List[Document], callbacks: Callbacks = None, **kwargs: Any
    ) -> Tuple[str, dict]:
        """Stuff all documents into one prompt and pass to LLM.

        Args:
            docs: List of documents to join together into one variable
            callbacks: Optional callbacks to pass along
            **kwargs: additional parameters to use to get inputs to LLMChain.

        Returns:
            The first element returned is the single string output. The second
            element returned is a dictionary of other keys to return.
        """
        inputs = self._get_inputs(docs, **kwargs)
        # Call predict on the LLM.
        return self.llm_chain.predict(callbacks=callbacks, **inputs), {}

    ...

class Chain(RunnableSerializable[Dict[str, Any], Dict[str, Any]], ABC):
    """Abstract base class for creating structured sequences of calls to components.

    Chains should be used to encode a sequence of calls to components like
    models, document retrievers, other chains, etc., and provide a simple interface
    to this sequence.

    The Chain interface makes it easy to create apps that are:
        - Stateful: add Memory to any Chain to give it state,
        - Observable: pass Callbacks to a Chain to execute additional functionality,
            like logging, outside the main sequence of component calls,
        - Composable: the Chain API is flexible enough that it is easy to combine
            Chains with other components, including other Chains.

    The main methods exposed by chains are:
        - `__call__`: Chains are callable. The `__call__` method is the primary way to
            execute a Chain. This takes inputs as a dictionary and returns a
            dictionary output.
        - `run`: A convenience method that takes inputs as args/kwargs and returns the
            output as a string or object. This method can only be used for a subset of
            chains and cannot return as rich of an output as `__call__`.
    """
    ...
    def invoke(
        self,
        input: Dict[str, Any],
        config: Optional[RunnableConfig] = None,
        **kwargs: Any,
    ) -> Dict[str, Any]:
        config = ensure_config(config)
        callbacks = config.get("callbacks")
        tags = config.get("tags")
        metadata = config.get("metadata")
        run_name = config.get("run_name") or self.get_name()
        include_run_info = kwargs.get("include_run_info", False)
        return_only_outputs = kwargs.get("return_only_outputs", False)

        inputs = self.prep_inputs(input)
        callback_manager = CallbackManager.configure(
            callbacks,
            self.callbacks,
            self.verbose,
            tags,
            self.tags,
            metadata,
            self.metadata,
        )
        new_arg_supported = inspect.signature(self._call).parameters.get("run_manager")

        run_manager = callback_manager.on_chain_start(
            dumpd(self),
            inputs,
            name=run_name,
        )
        try:
            self._validate_inputs(inputs)
            outputs = (
                self._call(inputs, run_manager=run_manager)
                if new_arg_supported
                else self._call(inputs)
            )

            final_outputs: Dict[str, Any] = self.prep_outputs(
                inputs, outputs, return_only_outputs
            )
        except BaseException as e:
            run_manager.on_chain_error(e)
            raise e
        run_manager.on_chain_end(outputs)

        if include_run_info:
            final_outputs[RUN_KEY] = RunInfo(run_id=run_manager.run_id)
        return final_outputs

class BaseCombineDocumentsChain(Chain, ABC):
    """Base interface for chains combining documents.

    Subclasses of this chain deal with combining documents in a variety of
    ways. This base class exists to add some uniformity in the interface these types
    of chains should expose. Namely, they expect an input key related to the documents
    to use (default `input_documents`), and then also expose a method to calculate
    the length of a prompt from documents (useful for outside callers to use to
    determine whether it's safe to pass a list of documents into this chain or whether
    that will be longer than the context length).
    """
    ...
    def _call(
        self,
        inputs: Dict[str, List[Document]],
        run_manager: Optional[CallbackManagerForChainRun] = None,
    ) -> Dict[str, str]:
        """Prepare inputs, call combine docs, prepare outputs."""
        _run_manager = run_manager or CallbackManagerForChainRun.get_noop_manager()
        docs = inputs[self.input_key]
        # Other keys are assumed to be needed for LLM prediction
        other_keys = {k: v for k, v in inputs.items() if k != self.input_key}
        output, extra_return_dict = self.combine_docs(
            docs, callbacks=_run_manager.get_child(), **other_keys
        )
        extra_return_dict[self.output_key] = output
        return extra_return_dict

Chain <- RunnableSerializable <- Serializable <- BaseModel