context_editing.py — langchain Source File

Source Code

"""Context editing middleware.

Mirrors Anthropic's context editing capabilities by clearing older tool results once the
conversation grows beyond a configurable token threshold.

The implementation is intentionally model-agnostic so it can be used with any LangChain
chat model.
"""

from __future__ import annotations

from collections.abc import Awaitable, Callable, Iterable, Sequence
from copy import deepcopy
from dataclasses import dataclass
from typing import Literal

from langchain_core.messages import (
    AIMessage,
    AnyMessage,
    BaseMessage,
    ToolMessage,
)
from langchain_core.messages.utils import count_tokens_approximately
from typing_extensions import Protocol

from langchain.agents.middleware.types import (
    AgentMiddleware,
    AgentState,
    ContextT,
    ModelRequest,
    ModelResponse,
    ResponseT,
)

DEFAULT_TOOL_PLACEHOLDER = "[cleared]"


TokenCounter = Callable[
    [Sequence[BaseMessage]],
    int,
]


class ContextEdit(Protocol):
    """Protocol describing a context editing strategy."""

    def apply(
        self,
        messages: list[AnyMessage],
        *,
        count_tokens: TokenCounter,
    ) -> None:
        """Apply an edit to the message list in place."""
        ...


@dataclass(slots=True)
class ClearToolUsesEdit(ContextEdit):
    """Configuration for clearing tool outputs when token limits are exceeded."""

// ... (239 more lines)