chat_history.py — langchain Source File

Source Code

"""Chat message history stores a history of the message interactions in a chat."""

from __future__ import annotations

from abc import ABC, abstractmethod
from typing import TYPE_CHECKING

from pydantic import BaseModel, Field

from langchain_core.messages import (
    AIMessage,
    BaseMessage,
    HumanMessage,
    get_buffer_string,
)
from langchain_core.runnables.config import run_in_executor

if TYPE_CHECKING:
    from collections.abc import Sequence


class BaseChatMessageHistory(ABC):
    """Abstract base class for storing chat message history.

    Implementations guidelines:

    Implementations are expected to over-ride all or some of the following methods:

    * `add_messages`: sync variant for bulk addition of messages
    * `aadd_messages`: async variant for bulk addition of messages
    * `messages`: sync variant for getting messages
    * `aget_messages`: async variant for getting messages
    * `clear`: sync variant for clearing messages
    * `aclear`: async variant for clearing messages

    `add_messages` contains a default implementation that calls `add_message`
    for each message in the sequence. This is provided for backwards compatibility
    with existing implementations which only had `add_message`.

    Async variants all have default implementations that call the sync variants.
    Implementers can choose to override the async implementations to provide
    truly async implementations.

    Usage guidelines:

    When used for updating history, users should favor usage of `add_messages`
    over `add_message` or other variants like `add_user_message` and `add_ai_message`
    to avoid unnecessary round-trips to the underlying persistence layer.

    Example:
        ```python
        import json
        import os
        from langchain_core.messages import messages_from_dict, message_to_dict


        class FileChatMessageHistory(BaseChatMessageHistory):
            storage_path: str
            session_id: str

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