few_shot_prompt and placeholder in a ChatPromptTemplate, an error occurred, any help?

[lzunx]

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Example Code

from src.utils.examples import create_few_shot_prompt
from src.utils.llm import llm_gpt4o
examples = [
    {"input": "2 🦜 2", "output": "4"},
    {"input": "2 🦜 3", "output": "5"},
    {"input": "2 🦜 4", "output": "6"},
    {"input": "What did the cow say to the moon?", "output": "nothing at all"},
    {
        "input": "Write me a poem about the moon",
        "output": "One for the moon, and one for me, who are we to talk about the moon?",
    },
]
#create_few_shot_prompt is a method extracted from official docs, 
#[🦜️🔗 LangChain](https://python.langchain.com/docs/how_to/few_shot_examples_chat/)

def create_few_shot_prompt(examples):
    to_vectorize = [" ".join(example.values()) for example in examples]
    vectorstore = Chroma.from_texts(to_vectorize, openai_embeddings, metadatas=examples)

    example_selector = SemanticSimilarityExampleSelector(
        vectorstore=vectorstore,
        k=2,
    )

    few_shot_prompt = FewShotChatMessagePromptTemplate(
        input_variables=["question"],
        example_selector=example_selector,
        example_prompt=ChatPromptTemplate.from_messages(
            [("human", "{input}"), ("ai", "{output}")]
        ),
    )

    return few_shot_prompt

final_prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "You are a wondrous wizard of math."),
        create_few_shot_prompt(examples),
        ("placeholder", "{messages}"),
        ("human", "{question}"),
    ]
)

print(final_prompt.input_variables)
print(final_prompt.optional_variables)
print(final_prompt.partial_variables)

chain = final_prompt | llm_gpt4o

chain.invoke({"question": "What's 3 🦜 3?"})

Description

If I delete ("placeholder", "{messages}"), there will be no error, how can I make the two coexist?

python3.11/site-packages/langchain_core/runnables/base.py:1927, in Runnable._call_with_config(self, func, input, config, run_type, serialized, **kwargs)...     56     return " ".join(sorted_values({key: example[key] for key in input_keys}))
     57 else:
---> 58     return " ".join(sorted_values(example))

TypeError: sequence item 0: expected str instance, list found

System Info

langchain==0.3.9
langchain-chroma==0.1.4
langchain-community==0.3.8
langchain-core==0.3.21
langchain-openai==0.2.10
langchain-text-splitters==0.3.2

Linux Ubuntu 24
python==3.11

[feijoes]

[lzunx]

I want a way for them to exist simultaneously, now the approach I take is to convert few shots into strings and then fill them into ("system", "{examples_str}").
What I really want is for few_shot_prompt to work with ("placeholder", "{messages}") in a ChatPromptTemplate without errors.

[lzunx]

@bracesproul @efriis
Hello, sorry to bother you. Due to some confidentiality regulations, I need to delete all traces from my GitHub. Could you please delete this discussion?