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# Source code for langchain.agents.conversational_chat.base

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

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

    from langchain_core._api import deprecated
    from langchain_core.agents import AgentAction
    from langchain_core.callbacks import BaseCallbackManager
    from langchain_core.language_models import BaseLanguageModel
    from langchain_core.messages import AIMessage, BaseMessage, HumanMessage
    from langchain_core.output_parsers import BaseOutputParser
    from langchain_core.prompts import BasePromptTemplate
    from langchain_core.prompts.chat import (
        ChatPromptTemplate,
        HumanMessagePromptTemplate,
        MessagesPlaceholder,
        SystemMessagePromptTemplate,
    )
    from langchain_core.pydantic_v1 import Field
    from langchain_core.tools import BaseTool

    from langchain.agents.agent import Agent, AgentOutputParser
    from langchain.agents.conversational_chat.output_parser import ConvoOutputParser
    from langchain.agents.conversational_chat.prompt import (
        PREFIX,
        SUFFIX,
        TEMPLATE_TOOL_RESPONSE,
    )
    from langchain.agents.utils import validate_tools_single_input
    from langchain.chains import LLMChain

    @deprecated("0.1.0", alternative="create_json_chat_agent", removal="0.3.0")
    class ConversationalChatAgent(Agent):
        """An agent designed to hold a conversation in addition to using tools."""

        output_parser: AgentOutputParser = Field(default_factory=ConvoOutputParser)
        template_tool_response: str = TEMPLATE_TOOL_RESPONSE

        @classmethod
        def _get_default_output_parser(cls, **kwargs: Any) -> AgentOutputParser:
            return ConvoOutputParser()

        @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 _validate_tools(cls, tools: Sequence[BaseTool]) -> None:
            super()._validate_tools(tools)
            validate_tools_single_input(cls.__name__, tools)

        @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 cls._get_default_output_parser()
            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)  # type: ignore[arg-type]

        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=self.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,
            output_parser: Optional[AgentOutputParser] = None,
            system_message: str = PREFIX,
            human_message: str = SUFFIX,
            input_variables: Optional[List[str]] = None,
            **kwargs: Any,
        ) -> Agent:
            """Construct an agent from an LLM and tools."""
            cls._validate_tools(tools)
            _output_parser = output_parser or cls._get_default_output_parser()
            prompt = cls.create_prompt(
                tools,
                system_message=system_message,
                human_message=human_message,
                input_variables=input_variables,
                output_parser=_output_parser,
            )
            llm_chain = LLMChain(  # type: ignore[misc]
                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,
            )