src/agents/functions_agent/base.py

from typing import Sequence

from langchain_core.language_models import BaseLanguageModel
from langchain_core.prompts.chat import ChatPromptTemplate
from langchain_core.runnables import Runnable, RunnablePassthrough
from langchain_core.tools import BaseTool

from agents.format_scratchpad.functions import (
   format_to_function_messages,
)
from agents.output_parsers.functions import (
   FunctionsAgentOutputParser,
)

def create_functions_agent(
   llm: BaseLanguageModel, prompt: ChatPromptTemplate
) -> Runnable:
   """Create an agent that uses function calling.

   Args:
       llm: LLM to use as the agent. Should work with Nous Hermes function calling,
           so either be an Nous Hermes based model that supports that or a wrapper of
           a different model that adds in equivalent support.
       prompt: The prompt to use. See Prompt section below for more.

   Returns:
       A Runnable sequence representing an agent. It takes as input all the same input
       variables as the prompt passed in does. It returns as output either an
       AgentAction or AgentFinish.
   """
   if "agent_scratchpad" not in (
       prompt.input_variables + list(prompt.partial_variables)
   ):
       raise ValueError(
           "Prompt must have input variable `agent_scratchpad`, but wasn't found."
           f"Found {prompt.input_variables} instead."
       )
   agent = (
       RunnablePassthrough.assign(
           agent_scratchpad=lambda x: format_to_function_messages(
               x["intermediate_steps"]
           )
       )
       | prompt
       | llm
       | FunctionsAgentOutputParser()
   )
   return agent