[Solved] Given this LangChain code snippet, what will be printed when the chain runs? from langchain.callbacks.... Given this LangChain code snippet, what will be printed when the chain runs? | LangChain

LangChain - LangSmith Observability

Given this LangChain code snippet, what will be printed when the chain runs?

from langchain.callbacks.base import BaseCallbackHandler

class PrintCallback(BaseCallbackHandler):
    def on_llm_start(self, serialized, prompts, **kwargs):
        print(f"LLM started with prompt: {prompts[0]}")

chain = LLMChain(llm=llm, prompt=prompt, callbacks=[PrintCallback()])
chain.run("Hello")

ALLM started with prompt: Hello

BLLM started with prompt: ["Hello"]

CNo output printed

DError: on_llm_start method missing required arguments

Step-by-Step Solution

Solution:

Step 1: Understand the on_llm_start callback parameter
The 'prompts' argument is a list of prompt strings, so prompts[0] is the first prompt string.
Step 2: Analyze the print statement output
The print outputs the string with prompts[0], which is the string "Hello" passed to run, but wrapped in a list originally.
Final Answer:
LLM started with prompt: Hello -> Option A
Quick Check:
Print prompt string = "Hello" [OK]

Quick Trick: Callbacks receive prompts as list; print first item for prompt text [OK]

Common Mistakes:

MISTAKES

Thinking prompts is a string, not a list
Expecting no output from callback
Confusing method parameters causing errors

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Given this LangChain code snippet, what will be printed when the chain runs?

Step 1: Understand the on_llm_start callback parameter

Step 2: Analyze the print statement output

Final Answer:

Quick Check:

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