[Solved] You run this code and get an AttributeError: 'NoneType' object has no attribute 'total_tokens'. What is the most probable reason?cb = get_openai_callback() chain.run("Example") print(cb.total_tokens) | LangChain

LangChain - LangSmith Observability

You run this code and get an AttributeError: 'NoneType' object has no attribute 'total_tokens'. What is the most probable reason?

cb = get_openai_callback()
chain.run("Example")
print(cb.total_tokens)

AThe callback was not used as a context manager, so <code>cb</code> is None

BThe chain did not generate any tokens, so <code>total_tokens</code> is missing

CThe <code>get_openai_callback()</code> function is deprecated and returns None

DThe <code>total_tokens</code> attribute is private and cannot be accessed directly

Step-by-Step Solution

Solution:

Step 1: Understand how get_openai_callback() works
It is designed to be used as a context manager to properly initialize and finalize tracking.
Step 2: Analyze the code
Here, cb is assigned the return value of get_openai_callback() without a with statement, which returns None.
Step 3: Reason about the error
Since cb is None, accessing total_tokens raises AttributeError.
Final Answer:
The callback was not used as a context manager, so cb is None -> Option A
Quick Check:
Always use get_openai_callback() with with [OK]

Quick Trick: Use get_openai_callback() as context manager [OK]

Common Mistakes:

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You run this code and get an AttributeError: 'NoneType' object has no attribute 'total_tokens'. What is the most probable reason?