__init__() — langchain Function Reference

Source Code

libs/core/langchain_core/runnables/history.py lines 249–373

    def __init__(
        self,
        runnable: Runnable[
            list[BaseMessage], str | BaseMessage | MessagesOrDictWithMessages
        ]
        | Runnable[dict[str, Any], str | BaseMessage | MessagesOrDictWithMessages]
        | LanguageModelLike,
        get_session_history: GetSessionHistoryCallable,
        *,
        input_messages_key: str | None = None,
        output_messages_key: str | None = None,
        history_messages_key: str | None = None,
        history_factory_config: Sequence[ConfigurableFieldSpec] | None = None,
        **kwargs: Any,
    ) -> None:
        """Initialize `RunnableWithMessageHistory`.

        Args:
            runnable: The base `Runnable` to be wrapped.

                Must take as input one of:

                1. A list of `BaseMessage`
                2. A `dict` with one key for all messages
                3. A `dict` with one key for the current input string/message(s) and
                    a separate key for historical messages. If the input key points
                    to a string, it will be treated as a `HumanMessage` in history.

                Must return as output one of:

                1. A string which can be treated as an `AIMessage`
                2. A `BaseMessage` or sequence of `BaseMessage`
                3. A `dict` with a key for a `BaseMessage` or sequence of
                    `BaseMessage`

            get_session_history: Function that returns a new `BaseChatMessageHistory`.

                This function should either take a single positional argument
                `session_id` of type string and return a corresponding
                chat message history instance.

                ```python
                def get_session_history(
                    session_id: str, *, user_id: str | None = None
                ) -> BaseChatMessageHistory: ...
                ```

                Or it should take keyword arguments that match the keys of
                `session_history_config_specs` and return a corresponding
                chat message history instance.

                ```python
                def get_session_history(
                    *,
                    user_id: str,
                    thread_id: str,
                ) -> BaseChatMessageHistory: ...
                ```

            input_messages_key: Must be specified if the base runnable accepts a `dict`
                as input.
            output_messages_key: Must be specified if the base runnable returns a `dict`
                as output.
            history_messages_key: Must be specified if the base runnable accepts a
                `dict` as input and expects a separate key for historical messages.
            history_factory_config: Configure fields that should be passed to the
                chat history factory. See `ConfigurableFieldSpec` for more details.

                Specifying these allows you to pass multiple config keys into the
                `get_session_history` factory.
            **kwargs: Arbitrary additional kwargs to pass to parent class
                `RunnableBindingBase` init.

        """
        history_chain: Runnable[Any, Any] = RunnableLambda(
            self._enter_history, self._aenter_history
        ).with_config(run_name="load_history")
        messages_key = history_messages_key or input_messages_key
        if messages_key:
            history_chain = RunnablePassthrough.assign(
                **{messages_key: history_chain}