langchain/langchain/agents/conversational_chat/base.py

"""An agent designed to hold a conversation in addition to using tools."""
from __future__ import annotations

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

from langchain.agents.agent import Agent
from langchain.agents.conversational_chat.prompt import (
    FORMAT_INSTRUCTIONS,
    PREFIX,
    SUFFIX,
    TEMPLATE_TOOL_RESPONSE,
)
from langchain.callbacks.base import BaseCallbackManager
from langchain.chains import LLMChain
from langchain.output_parsers.base import BaseOutputParser
from langchain.prompts.base import BasePromptTemplate
from langchain.prompts.chat import (
    ChatPromptTemplate,
    HumanMessagePromptTemplate,
    MessagesPlaceholder,
    SystemMessagePromptTemplate,
)
from langchain.schema import (
    AgentAction,
    AIMessage,
    BaseLanguageModel,
    BaseMessage,
    HumanMessage,
)
from langchain.tools.base import BaseTool


class AgentOutputParser(BaseOutputParser):
    def get_format_instructions(self) -> str:
        return FORMAT_INSTRUCTIONS

    def parse(self, text: str) -> Any:
        cleaned_output = text.strip()
        if "```json" in cleaned_output:
            _, cleaned_output = cleaned_output.split("```json")
        if cleaned_output.startswith("```json"):
            cleaned_output = cleaned_output[len("```json") :]
        if cleaned_output.startswith("```"):
            cleaned_output = cleaned_output[len("```") :]
        if cleaned_output.endswith("```"):
            cleaned_output = cleaned_output[: -len("```")]
        cleaned_output = cleaned_output.strip()
        response = json.loads(cleaned_output)
        return {"action": response["action"], "action_input": response["action_input"]}


class ConversationalChatAgent(Agent):
    """An agent designed to hold a conversation in addition to using tools."""

    output_parser: BaseOutputParser

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

    @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:"

    @classmethod
    def create_prompt(
        cls,
        tools: Sequence[BaseTool],
        system_message: str = PREFIX,
        human_message: str = SUFFIX,
        input_variables: Optional[List[str]] = None,
        output_parser: Optional[BaseOutputParser] = None,
    ) -> BasePromptTemplate:
        tool_strings = "\n".join(
            [f"> {tool.name}: {tool.description}" for tool in tools]
        )
        tool_names = ", ".join([tool.name for tool in tools])
        _output_parser = output_parser or AgentOutputParser()
        format_instructions = human_message.format(
            format_instructions=_output_parser.get_format_instructions()
        )
        final_prompt = format_instructions.format(
            tool_names=tool_names, tools=tool_strings
        )
        if input_variables is None:
            input_variables = ["input", "chat_history", "agent_scratchpad"]
        messages = [
            SystemMessagePromptTemplate.from_template(system_message),
            MessagesPlaceholder(variable_name="chat_history"),
            HumanMessagePromptTemplate.from_template(final_prompt),
            MessagesPlaceholder(variable_name="agent_scratchpad"),
        ]
        return ChatPromptTemplate(input_variables=input_variables, messages=messages)

    def _extract_tool_and_input(self, llm_output: str) -> Optional[Tuple[str, str]]:
        try:
            response = self.output_parser.parse(llm_output)
            return response["action"], response["action_input"]
        except Exception:
            raise ValueError(f"Could not parse LLM output: {llm_output}")

    def _construct_scratchpad(
        self, intermediate_steps: List[Tuple[AgentAction, str]]
    ) -> List[BaseMessage]:
        """Construct the scratchpad that lets the agent continue its thought process."""
        thoughts: List[BaseMessage] = []
        for action, observation in intermediate_steps:
            thoughts.append(AIMessage(content=action.log))
            human_message = HumanMessage(
                content=TEMPLATE_TOOL_RESPONSE.format(observation=observation)
            )
            thoughts.append(human_message)
        return thoughts

    @classmethod
    def from_llm_and_tools(
        cls,
        llm: BaseLanguageModel,
        tools: Sequence[BaseTool],
        callback_manager: Optional[BaseCallbackManager] = None,
        system_message: str = PREFIX,
        human_message: str = SUFFIX,
        input_variables: Optional[List[str]] = None,
        output_parser: Optional[BaseOutputParser] = None,
        **kwargs: Any,
    ) -> Agent:
        """Construct an agent from an LLM and tools."""
        cls._validate_tools(tools)
        _output_parser = output_parser or AgentOutputParser()
        prompt = cls.create_prompt(
            tools,
            system_message=system_message,
            human_message=human_message,
            input_variables=input_variables,
            output_parser=_output_parser,
        )
        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,
            output_parser=_output_parser,
            **kwargs,
        )