Following Build A Chatbot Tutorial: SystemMessage Error in Trimming

[Miguel-Adarlo]

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Example Code

import getpass
import os
from operator import itemgetter
from langchain_core.messages import HumanMessage, AIMessage, SystemMessage, trim_messages
from langchain_core.runnables import RunnablePassthrough
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.chat_history import (
    BaseChatMessageHistory,
    InMemoryChatMessageHistory,
)
from langchain_core.runnables.history import RunnableWithMessageHistory

os.environ["GOOGLE_API_KEY"] = getpass.getpass()

from langchain_google_vertexai import ChatVertexAI

model = ChatVertexAI(model="gemini-pro")

store = {}

def get_session_history(session_id: str) -> BaseChatMessageHistory:
    if session_id not in store:
        store[session_id] = InMemoryChatMessageHistory()
    return store[session_id]

prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You are a helpful assistant. Answer all questions to the best of your ability in {language}.",
        ),
        MessagesPlaceholder(variable_name="messages"), #Where your messages go to.
    ]
)

trimmer = trim_messages( #Documentation: https://api.python.langchain.com/en/latest/messages/langchain_core.messages.utils.trim_messages.html
    max_tokens=65,
    strategy="last",
    token_counter=model,
    include_system=True, 
    allow_partial=False,
    start_on="human",
)

messages = [
    SystemMessage(content="you're a good assistant"), #kept this
    HumanMessage(content="hi! I'm bob"),
    AIMessage(content="hi!"),
    HumanMessage(content="I like vanilla ice cream"),
    AIMessage(content="nice"),
    HumanMessage(content="whats 2 + 2"), #history starts here.
    AIMessage(content="4"),
    HumanMessage(content="thanks"),
    AIMessage(content="no problem!"),
    HumanMessage(content="having fun?"),
    AIMessage(content="yes!"),
]
chain = (
    RunnablePassthrough.assign(messages=itemgetter("messages") | trimmer)
    | prompt
    | model
)

response = chain.invoke(
    {
        "messages": messages + [HumanMessage(content="what's my name?")],
        "language": "English",
    }
)

Description

I'm trying to follow the tutorial on Langchain Chatbots. I'm at the trimming part. I run into this error:
`
ValueError Traceback (most recent call last)
File /Users/xxxxxx/Documents/VINA-FRIDAY/ChatbotTest.py:69
50 messages = [
51 SystemMessage(content="you're a good assistant"), #kept this
52 HumanMessage(content="hi! I'm bob"),
(...)
61 AIMessage(content="yes!"),
62 ]
63 chain = (
64 RunnablePassthrough.assign(messages=itemgetter("messages") | trimmer)
65 | prompt
66 | model
67 )
---> 69 response = chain.invoke(
70 {
71 "messages": messages + [HumanMessage(content="what's my name?")],
72 "language": "English",
73 }
74 )

File ~/anaconda3/envs/VINA-FRIDAY/lib/python3.11/site-packages/langchain_core/runnables/base.py:2499, in RunnableSequence.invoke(self, input, config, **kwargs)
2497 input = step.invoke(input, config, **kwargs)
2498 else:
-> 2499 input = step.invoke(input, config)
...
257 "Detected more than one SystemMessage in the list of messages."
258 "Gemini APIs support the insertion of only one SystemMessage."
259 )

ValueError: SystemMessage should be the first in the history.
`

When trying to reset the prompt to not have a system message, it doesn't work. I still have the same error.

System Info

langchain==0.2.7
langchain-community==0.2.6
langchain-core==0.2.12
langchain-google-vertexai==1.0.6
langchain-text-splitters==0.2.2

Mac
Python 3.11

[DiegoRamos-SB]

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