langchain/langchain/agents/chat/base.py

import json
from typing import Any, List, Optional, Sequence, Tuple

from langchain.agents.agent import Agent
from langchain.agents.chat.prompt import FORMAT_INSTRUCTIONS, PREFIX, SUFFIX
from langchain.callbacks.base import BaseCallbackManager
from langchain.chains.llm import LLMChain
from langchain.prompts.base import BasePromptTemplate
from langchain.prompts.chat import (
    ChatPromptTemplate,
    HumanMessagePromptTemplate,
    SystemMessagePromptTemplate,
)
from langchain.schema import AgentAction, BaseLanguageModel
from langchain.tools import BaseTool

FINAL_ANSWER_ACTION = "Final Answer:"


class ChatAgent(Agent):
    @property
    def observation_prefix(self) -> str:
        """Prefix to append the observation with."""
        return "Observation: "

    @property
    def llm_prefix(self) -> str:
        """Prefix to append the llm call with."""
        return "Thought:"

    def _construct_scratchpad(
        self, intermediate_steps: List[Tuple[AgentAction, str]]
    ) -> str:
        agent_scratchpad = super()._construct_scratchpad(intermediate_steps)
        if agent_scratchpad:
            return (
                f"This was your previous work "
                f"(but I haven't seen any of it! I only see what "
                f"you return as final answer):\n{agent_scratchpad}"
            )
        else:
            return agent_scratchpad

    def _extract_tool_and_input(self, text: str) -> Optional[Tuple[str, str]]:
        if FINAL_ANSWER_ACTION in text:
            return "Final Answer", text.split(FINAL_ANSWER_ACTION)[-1].strip()
        try:
            _, action, _ = text.split("```")
            response = json.loads(action.strip())
            return response["action"], response["action_input"]

        except Exception:
            raise ValueError(f"Could not parse LLM output: {text}")

    @property
    def _stop(self) -> List[str]:
        return ["Observation:"]

    @classmethod
    def create_prompt(
        cls,
        tools: Sequence[BaseTool],
        prefix: str = PREFIX,
        suffix: str = SUFFIX,
        format_instructions: str = FORMAT_INSTRUCTIONS,
        input_variables: Optional[List[str]] = None,
    ) -> BasePromptTemplate:
        tool_strings = "\n".join([f"{tool.name}: {tool.description}" for tool in tools])
        tool_names = ", ".join([tool.name for tool in tools])
        format_instructions = format_instructions.format(tool_names=tool_names)
        template = "\n\n".join([prefix, tool_strings, format_instructions, suffix])
        messages = [
            SystemMessagePromptTemplate.from_template(template),
            HumanMessagePromptTemplate.from_template("{input}\n\n{agent_scratchpad}"),
        ]
        return ChatPromptTemplate(
            input_variables=["input", "agent_scratchpad"], messages=messages
        )

    @classmethod
    def from_llm_and_tools(
        cls,
        llm: BaseLanguageModel,
        tools: Sequence[BaseTool],
        callback_manager: Optional[BaseCallbackManager] = None,
        prefix: str = PREFIX,
        suffix: str = SUFFIX,
        format_instructions: str = FORMAT_INSTRUCTIONS,
        input_variables: Optional[List[str]] = None,
        **kwargs: Any,
    ) -> Agent:
        """Construct an agent from an LLM and tools."""
        cls._validate_tools(tools)
        prompt = cls.create_prompt(
            tools,
            prefix=prefix,
            suffix=suffix,
            format_instructions=format_instructions,
            input_variables=input_variables,
        )
        llm_chain = LLMChain(
            llm=llm,
            prompt=prompt,
            callback_manager=callback_manager,
        )
        tool_names = [tool.name for tool in tools]
        return cls(llm_chain=llm_chain, allowed_tools=tool_names, **kwargs)

    @property
    def _agent_type(self) -> str:
        raise ValueError