file.py — langchain Source File

Source Code

"""Callback handler that writes to a file."""

from __future__ import annotations

from pathlib import Path
from typing import TYPE_CHECKING, Any, TextIO, cast

from typing_extensions import Self, override

from langchain_core._api import warn_deprecated
from langchain_core.callbacks import BaseCallbackHandler
from langchain_core.utils.input import print_text

if TYPE_CHECKING:
    from langchain_core.agents import AgentAction, AgentFinish


_GLOBAL_DEPRECATION_WARNED = False


class FileCallbackHandler(BaseCallbackHandler):
    """Callback handler that writes to a file.

    This handler supports both context manager usage (recommended) and direct
    instantiation (deprecated) for backwards compatibility.

    Examples:
        Using as a context manager (recommended):

        ```python
        with FileCallbackHandler("output.txt") as handler:
            # Use handler with your chain/agent
            chain.invoke(inputs, config={"callbacks": [handler]})
        ```

        Direct instantiation (deprecated):

        ```python
        handler = FileCallbackHandler("output.txt")
        # File remains open until handler is garbage collected
        try:
            chain.invoke(inputs, config={"callbacks": [handler]})
        finally:
            handler.close()  # Explicit cleanup recommended
        ```

    Args:
        filename: The file path to write to.
        mode: The file open mode. Defaults to `'a'` (append).
        color: Default color for text output.

    !!! note

        When not used as a context manager, a deprecation warning will be issued on
        first use. The file will be opened immediately in `__init__` and closed in
        `__del__` or when `close()` is called explicitly.

    """

    def __init__(
// ... (208 more lines)