AsyncLangchainCallbackHandler IndexError when agent calls a tool

I'm getting an IndexError: list index out of range from AsyncLangchainCallbackHandler when the agent calls a tool; I'm using chainlit 0.6.3.


import chainlit as cl

from langchain.agents import Tool, AgentExecutor, OpenAIFunctionsAgent
from langchain.schema import SystemMessage
from langchain.chat_models import ChatOpenAI
from pydantic.v1 import BaseModel, Field

class GetWordLength(BaseModel):
    word: str = Field(description="word to calculate length for")

async def get_word_length(word: str) -> int:
    """Returns the length of a word."""
    print('calculating length')
    return len(word)

@cl.on_chat_start
def main():
    tools = [Tool.from_function(
        func=get_word_length,
        name="GetWordLength",
        description="calculates the length of a word",
        args_schema=GetWordLength,
        coroutine=get_word_length
    )]

    llm = ChatOpenAI(temperature=0)
    prompt = OpenAIFunctionsAgent.create_prompt(
        system_message=SystemMessage(content="be useful")
    )
    agent = OpenAIFunctionsAgent(llm=llm, tools=tools, prompt=prompt)
    executor = AgentExecutor(agent=agent, tools=tools, verbose=True)

    cl.user_session.set("executor", executor)

@cl.on_message
async def main(message: str):
    llm_chain = cl.user_session.get("executor")

    res = await llm_chain.arun(message, callbacks=[cl.AsyncLangchainCallbackHandler()])
    await cl.Message(content=res).send()

Question: how long is foobar

> Entering new AgentExecutor chain...
2023-08-26 08:09:58 - message='OpenAI API response' path=https://api.openai.com/v1/chat/completions processing_ms=550 request_id=6a13b82df2d603709a3bf3c087f27a6f response_code=200

Invoking: `GetWordLength` with `{'word': 'foobar'}`

calculating length
62023-08-26 08:09:58 - Error in AsyncLangchainCallbackHandler.on_chat_model_start callback: list index out of range
2023-08-26 08:09:58 - list index out of range
Traceback (most recent call last):
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/chainlit/utils.py", line 36, in wrapper
    return await user_function(**params_values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/litpoc.py", line 44, in main
    res = await llm_chain.arun(message, callbacks=[cl.AsyncLangchainCallbackHandler()])
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chains/base.py", line 549, in arun
    await self.acall(
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chains/base.py", line 349, in acall
    raise e
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chains/base.py", line 343, in acall
    await self._acall(inputs, run_manager=run_manager)
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/agents/agent.py", line 1085, in _acall
    next_step_output = await self._atake_next_step(
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/agents/agent.py", line 929, in _atake_next_step
    output = await self.agent.aplan(
             ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/agents/openai_functions_agent/base.py", line 247, in aplan
    predicted_message = await self.llm.apredict_messages(
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chat_models/base.py", line 626, in apredict_messages
    return await self._call_async(messages, stop=_stop, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chat_models/base.py", line 566, in _call_async
    result = await self.agenerate(
             ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/chat_models/base.py", line 349, in agenerate
    run_managers = await callback_manager.on_chat_model_start(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/callbacks/manager.py", line 1432, in on_chat_model_start
    await asyncio.gather(*tasks)
  File "/usr/local/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/tasks.py", line 339, in __wakeup
    future.result()
  File "/usr/local/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/tasks.py", line 269, in __step
    result = coro.throw(exc)
             ^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/callbacks/manager.py", line 387, in _ahandle_event
    await asyncio.gather(
  File "/usr/local/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/tasks.py", line 339, in __wakeup
    future.result()
  File "/usr/local/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/asyncio/tasks.py", line 267, in __step
    result = coro.send(None)
             ^^^^^^^^^^^^^^^
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/callbacks/manager.py", line 372, in _ahandle_event_for_handler
    raise e
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/langchain/callbacks/manager.py", line 342, in _ahandle_event_for_handler
    await event(*args, **kwargs)
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/chainlit/langchain/callbacks.py", line 468, in on_chat_model_start
    _on_chat_model_start(self, serialized, messages, **kwargs)
  File "/Users/p8a/data/research/botpoc/venv/lib/python3.11/site-packages/chainlit/langchain/callbacks.py", line 254, in _on_chat_model_start
    self.current_prompt.messages[idx].formatted = m.content
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
IndexError: list index out of range

Chainlit / chainlit

AsyncLangchainCallbackHandler IndexError when agent calls a tool #328