langchain-output-formatting

Format LLM Output with Langchain on Jetson

Use Langchain's StructuredOutputParser to constrain LLM output into structured JSON for smart home control. The chatbot runs locally on Jetson using LlamaCpp with a Gradio web interface.

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Execution model

Run one phase at a time. After each phase:

• Relay all output to the user.
• If output contains [STOP] → stop, consult the failure decision tree.
• If output ends with [OK] → tell the user "Phase N complete" and proceed.

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Prerequisites

Requirement	Detail
Hardware	Jetson device (e.g. reComputer J4012)
JetPack	5.0+
Model	Llama 2 7B Chat GGUF (Q4_0 quantization)
Python	pip3 available

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Phase 1 — Install dependencies (~3 min)

pip3 install --no-cache-dir --verbose "langchain[llm]" openai
pip3 install --no-cache-dir --verbose gradio==3.38.0

[OK] when both packages install without error. [STOP] if pip3 fails — check Python version and pip availability.

---

Phase 2 — Download GGUF model (~5–15 min)

Download the Llama 2 7B Chat GGUF model (Q4_0 quantization) from Hugging Face:

mkdir -p ~/models
# Download llama-2-7b-chat.Q4_0.gguf from Hugging Face
# Example using wget or huggingface-cli:
pip3 install huggingface-hub
huggingface-cli download TheBloke/Llama-2-7B-Chat-GGUF llama-2-7b-chat.Q4_0.gguf --local-dir ~/models

Verify:

ls -lh ~/models/llama-2-7b-chat.Q4_0.gguf

[OK] when the GGUF file exists (~3.8 GB). [STOP] if download fails — check network and disk space.

---

Phase 3 — Create the chatbot script

Create format_opt.py with the following content. The script uses Langchain's StructuredOutputParser with ResponseSchema to define output fields (user_input, suggestion, control signal, temperature), then wraps a LlamaCpp model in a Gradio chat interface:

cat > format_opt.py << 'PYEOF'
import copy
import gradio as gr
from langchain.llms import LlamaCpp
from langchain.output_parsers import StructuredOutputParser, ResponseSchema
from langchain.prompts import PromptTemplate

class ChatBot:
    def __init__(self, llama_model_path, history_length=3):
        self.chat_history = []
        self.history_threshold = history_length
        self.llm = LlamaCpp(
            model_path=llama_model_path,
            temperature=0.75,
            max_tokens=2000,
            top_p=1
        )
        response_schemas = [
            ResponseSchema(name="user_input", description="This is the user's input"),
            ResponseSchema(name="suggestion", type="string", description="your suggestion"),
            ResponseSchema(name="control", description="This is your response"),
            ResponseSchema(name="temperature", type="int",
                           description="Degrees centigrade temperature of the air conditioner.")
        ]
        self.output_parser = StructuredOutputParser.from_response_schemas(response_schemas)
        self.format_instructions = self.output_parser.get_format_instructions()
        self.template = """
            Now you are a smart speaker, and you need to determine whether to turn on the air conditioner based on the user's input.
            In the suggestion section, please reply normal conversation.
            In the control section, if you need to turn on the air conditioner, please reply with <1>; if you need to turn off the air conditioner, please reply with <0>.
            {format_instructions}
            Please do not generate any comments.
            % USER INPUT:
            {user_input}
            YOUR RESPONSE:
        """
        self.prompt = PromptTemplate(
            input_variables=["user_input"],
            partial_variables={"format_instructions": self.format_instructions},
            template=self.template
        )

    def format_chat_prompt(self, message):
        prompt = ""
        for turn in self.chat_history:
            user_message, bot_message = turn
            prompt = f"{prompt}\nUser: {user_message}\nAssistant: {bot_message}"
        prompt = f"{prompt}\nUser: {message}\nAssistant:"
        return prompt

    def respond(self, message):
        prompt = self.prompt.format(user_input=message)
        formatted_prompt = self.format_chat_prompt(prompt)
        bot_message = self.llm(formatted_prompt)
        if len(self.chat_history) >= self.history_threshold:
            del self.chat_history[0]
        self.chat_history.append((message, bot_message))
        return "", self.chat_history

    def run_webui(self):
        with gr.Blocks() as demo:
            gr.Markdown("# Format Output of LLM Demo")
            chatbot = gr.Chatbot(height=500)
            msg = gr.Textbox(label="Prompt")
            btn = gr.Button("Submit")
            clear = gr.ClearButton(components=[msg, chatbot], value="Clear console")
            btn.click(self.respond, inputs=[msg], outputs=[msg, chatbot])
            msg.submit(self.respond, inputs=[msg], outputs=[msg, chatbot])
        gr.close_all()
        demo.launch()

if __name__ == '__main__':
    chatbot_ins = ChatBot("/home/nvidia/models/llama-2-7b-chat.Q4_0.gguf")
    chatbot_ins.run_webui()
PYEOF