agent.py — langchain Source File

Source Code

from __future__ import annotations

from collections.abc import Sequence

from langchain_core.language_models import BaseLanguageModel
from langchain_core.prompts import BasePromptTemplate
from langchain_core.runnables import Runnable, RunnablePassthrough
from langchain_core.tools import BaseTool
from langchain_core.tools.render import ToolsRenderer, render_text_description

from langchain_classic.agents import AgentOutputParser
from langchain_classic.agents.format_scratchpad import format_log_to_str
from langchain_classic.agents.output_parsers import ReActSingleInputOutputParser


def create_react_agent(
    llm: BaseLanguageModel,
    tools: Sequence[BaseTool],
    prompt: BasePromptTemplate,
    output_parser: AgentOutputParser | None = None,
    tools_renderer: ToolsRenderer = render_text_description,
    *,
    stop_sequence: bool | list[str] = True,
) -> Runnable:
    r"""Create an agent that uses ReAct prompting.

    Based on paper "ReAct: Synergizing Reasoning and Acting in Language Models"
    (https://arxiv.org/abs/2210.03629)

    !!! warning

        This implementation is based on the foundational ReAct paper but is older and
        not well-suited for production applications.

        For a more robust and feature-rich implementation, we recommend using the
        `create_agent` function from the `langchain` library.

        See the
        [reference doc](https://reference.langchain.com/python/langchain/agents/)
        for more information.

    Args:
        llm: LLM to use as the agent.
        tools: Tools this agent has access to.
        prompt: The prompt to use. See Prompt section below for more.
        output_parser: AgentOutputParser for parse the LLM output.
        tools_renderer: This controls how the tools are converted into a string and
            then passed into the LLM.
        stop_sequence: bool or list of str.
            If `True`, adds a stop token of "Observation:" to avoid hallucinates.
            If `False`, does not add a stop token.
            If a list of str, uses the provided list as the stop tokens.

            You may to set this to False if the LLM you are using
            does not support stop sequences.

    Returns:
        A Runnable sequence representing an agent. It takes as input all the same input
        variables as the prompt passed in does. It returns as output either an
        AgentAction or AgentFinish.
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