Toggle Menu
Prev Up Next

# Source code for langchain.agents.mrkl.base

    """Attempt to implement MRKL systems as described in arxiv.org/pdf/2205.00445.pdf."""
    from __future__ import annotations

    from typing import Any, Callable, List, NamedTuple, Optional, Sequence

    from langchain_core._api import deprecated
    from langchain_core.callbacks import BaseCallbackManager
    from langchain_core.language_models import BaseLanguageModel
    from langchain_core.prompts import PromptTemplate
    from langchain_core.pydantic_v1 import Field
    from langchain_core.tools import BaseTool, Tool

    from langchain.agents.agent import Agent, AgentExecutor, AgentOutputParser
    from langchain.agents.agent_types import AgentType
    from langchain.agents.mrkl.output_parser import MRKLOutputParser
    from langchain.agents.mrkl.prompt import FORMAT_INSTRUCTIONS, PREFIX, SUFFIX
    from langchain.agents.utils import validate_tools_single_input
    from langchain.chains import LLMChain
    from langchain.tools.render import render_text_description

    class ChainConfig(NamedTuple):
        """Configuration for chain to use in MRKL system.

        Args:
            action_name: Name of the action.
            action: Action function to call.
            action_description: Description of the action.
        """

        action_name: str
        action: Callable
        action_description: str

    @deprecated("0.1.0", alternative="create_react_agent", removal="0.3.0")
    class ZeroShotAgent(Agent):
        """Agent for the MRKL chain."""

        output_parser: AgentOutputParser = Field(default_factory=MRKLOutputParser)

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

        @property
        def _agent_type(self) -> str:
            """Return Identifier of agent type."""
            return AgentType.ZERO_SHOT_REACT_DESCRIPTION

        @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],
            prefix: str = PREFIX,
            suffix: str = SUFFIX,
            format_instructions: str = FORMAT_INSTRUCTIONS,
            input_variables: Optional[List[str]] = None,
        ) -> PromptTemplate:
            """Create prompt in the style of the zero shot agent.

            Args:
                tools: List of tools the agent will have access to, used to format the
                    prompt.
                prefix: String to put before the list of tools.
                suffix: String to put after the list of tools.
                input_variables: List of input variables the final prompt will expect.

            Returns:
                A PromptTemplate with the template assembled from the pieces here.
            """
            tool_strings = render_text_description(list(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])
            if input_variables:
                return PromptTemplate(template=template, input_variables=input_variables)
            return PromptTemplate.from_template(template)

        @classmethod
        def from_llm_and_tools(
            cls,
            llm: BaseLanguageModel,
            tools: Sequence[BaseTool],
            callback_manager: Optional[BaseCallbackManager] = None,
            output_parser: Optional[AgentOutputParser] = 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(  # type: ignore[misc]
                llm=llm,
                prompt=prompt,
                callback_manager=callback_manager,
            )
            tool_names = [tool.name for tool in tools]
            _output_parser = output_parser or cls._get_default_output_parser()
            return cls(
                llm_chain=llm_chain,
                allowed_tools=tool_names,
                output_parser=_output_parser,
                **kwargs,
            )

        @classmethod
        def _validate_tools(cls, tools: Sequence[BaseTool]) -> None:
            validate_tools_single_input(cls.__name__, tools)
            if len(tools) == 0:
                raise ValueError(
                    f"Got no tools for {cls.__name__}. At least one tool must be provided."
                )
            for tool in tools:
                if tool.description is None:
                    raise ValueError(
                        f"Got a tool {tool.name} without a description. For this agent, "
                        f"a description must always be provided."
                    )
            super()._validate_tools(tools)

    @deprecated("0.1.0", removal="0.3.0")
    class MRKLChain(AgentExecutor):
        """[Deprecated] Chain that implements the MRKL system."""

        @classmethod
        def from_chains(
            cls, llm: BaseLanguageModel, chains: List[ChainConfig], **kwargs: Any
        ) -> AgentExecutor:
            """User friendly way to initialize the MRKL chain.

            This is intended to be an easy way to get up and running with the
            MRKL chain.

            Args:
                llm: The LLM to use as the agent LLM.
                chains: The chains the MRKL system has access to.
                **kwargs: parameters to be passed to initialization.

            Returns:
                An initialized MRKL chain.
            """
            tools = [
                Tool(
                    name=c.action_name,
                    func=c.action,
                    description=c.action_description,
                )
                for c in chains
            ]
            agent = ZeroShotAgent.from_llm_and_tools(llm, tools)
            return cls(agent=agent, tools=tools, **kwargs)