LangChain Core Workflow (Python)

Overview

An engineer wires a four-stage LCEL chain: classify the question, retrieve context, format the prompt, invoke the LLM. It looks clean:

chain = (
    RunnablePassthrough.assign(category=classifier)
    | RunnablePassthrough.assign(docs=retriever)
    | prompt
    | llm
    | StrOutputParser()
)

chain.invoke({"question": "What's our refund policy?"})

The call returns this: