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"""Chain that takes in an input and produces an action and action input."""
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from __future__ import annotations
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from abc import ABC, abstractmethod
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from typing import Any, ClassVar, Dict, List, Optional, Tuple
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from pydantic import BaseModel
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from langchain.agents.input import ChainedInput
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from langchain.agents.tools import Tool
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from langchain.chains.base import Chain
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from langchain.chains.llm import LLMChain
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from langchain.input import get_color_mapping
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from langchain.llms.base import BaseLLM
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from langchain.prompts.base import BasePromptTemplate
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from langchain.schema import AgentAction
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class Agent(Chain, BaseModel, ABC):
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"""Agent that uses an LLM."""
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prompt: ClassVar[BasePromptTemplate]
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llm_chain: LLMChain
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tools: List[Tool]
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input_key: str = "input" #: :meta private:
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output_key: str = "output" #: :meta private:
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@property
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def input_keys(self) -> List[str]:
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"""Return the singular input key.
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:meta private:
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"""
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return [self.input_key]
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@property
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def output_keys(self) -> List[str]:
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"""Return the singular output key.
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:meta private:
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"""
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return [self.output_key]
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@property
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@abstractmethod
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def observation_prefix(self) -> str:
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"""Prefix to append the observation with."""
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@property
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@abstractmethod
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def llm_prefix(self) -> str:
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"""Prefix to append the LLM call with."""
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@property
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def finish_tool_name(self) -> str:
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"""Name of the tool to use to finish the chain."""
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return "Final Answer"
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@property
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def starter_string(self) -> str:
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"""Put this string after user input but before first LLM call."""
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return "\n"
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@abstractmethod
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def _extract_tool_and_input(self, text: str) -> Optional[Tuple[str, str]]:
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"""Extract tool and tool input from llm output."""
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def _fix_text(self, text: str) -> str:
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"""Fix the text."""
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raise ValueError("fix_text not implemented for this agent.")
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@property
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def _stop(self) -> List[str]:
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return [f"\n{self.observation_prefix}"]
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@classmethod
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def _validate_tools(cls, tools: List[Tool]) -> None:
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"""Validate that appropriate tools are passed in."""
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pass
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@classmethod
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def create_prompt(cls, tools: List[Tool]) -> BasePromptTemplate:
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"""Create a prompt for this class."""
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return cls.prompt
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def _prepare_for_new_call(self) -> None:
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pass
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@classmethod
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def from_llm_and_tools(
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cls, llm: BaseLLM, tools: List[Tool], **kwargs: Any
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) -> Agent:
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"""Construct an agent from an LLM and tools."""
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cls._validate_tools(tools)
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llm_chain = LLMChain(llm=llm, prompt=cls.create_prompt(tools))
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return cls(llm_chain=llm_chain, tools=tools, **kwargs)
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def get_action(self, text: str) -> AgentAction:
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"""Given input, decided what to do.
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Args:
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text: input string
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Returns:
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Action specifying what tool to use.
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"""
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input_key = self.llm_chain.input_keys[0]
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inputs = {input_key: text, "stop": self._stop}
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full_output = self.llm_chain.predict(**inputs)
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parsed_output = self._extract_tool_and_input(full_output)
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while parsed_output is None:
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full_output = self._fix_text(full_output)
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inputs = {input_key: text + full_output, "stop": self._stop}
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output = self.llm_chain.predict(**inputs)
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full_output += output
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parsed_output = self._extract_tool_and_input(full_output)
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tool, tool_input = parsed_output
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return AgentAction(tool, tool_input, full_output)
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def _call(self, inputs: Dict[str, str]) -> Dict[str, str]:
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"""Run text through and get agent response."""
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text = inputs[self.input_key]
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# Do any preparation necessary when receiving a new input.
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self._prepare_for_new_call()
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# Construct a mapping of tool name to tool for easy lookup
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name_to_tool_map = {tool.name: tool.func for tool in self.tools}
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# Construct the initial string to pass into the LLM. This is made up
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# of the user input, the special starter string, and then the LLM prefix.
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# The starter string is a special string that may be used by a LLM to
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# immediately follow the user input. The LLM prefix is a string that
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# prompts the LLM to take an action.
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starter_string = text + self.starter_string + self.llm_prefix
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# We use the ChainedInput class to iteratively add to the input over time.
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chained_input = ChainedInput(starter_string, verbose=self.verbose)
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# We construct a mapping from each tool to a color, used for logging.
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color_mapping = get_color_mapping(
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[tool.name for tool in self.tools], excluded_colors=["green"]
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)
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# We now enter the agent loop (until it returns something).
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while True:
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# Call the LLM to see what to do.
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output = self.get_action(chained_input.input)
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# Add the log to the Chained Input.
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chained_input.add_action(output, color="green")
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# If the tool chosen is the finishing tool, then we end and return.
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if output.tool == self.finish_tool_name:
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return {self.output_key: output.tool_input}
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# Otherwise we lookup the tool
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if output.tool in name_to_tool_map:
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chain = name_to_tool_map[output.tool]
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# We then call the tool on the tool input to get an observation
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observation = chain(output.tool_input)
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color = color_mapping[output.tool]
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else:
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observation = f"{output.tool} is not a valid tool, try another one."
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color = None
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# We then log the observation
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chained_input.add_observation(
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observation,
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self.observation_prefix,
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self.llm_prefix,
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color=color,
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)
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