Custom name of Span when using Langchain handler instead of RunnableSequence

[nathan-vo810]

Example when running the following code:

@observe()  # decorator to automatically log function as trace to Langfuse
def main():
    # get the langchain handler for the current trace
    langfuse_handler = langfuse_context.get_current_langchain_handler()
    # invoke chain with langfuse handler
    chain.invoke({"person": "Alan Turing"},
                 config={"callbacks": [langfuse_handler]})
 
main()

The displayed name for the span inside main trace will be RunnableSequence.

Is it possible to give another name to it?

[marcklingen]

Does his help? https://langfuse.com/docs/integrations/langchain/tracing#customizing-the-names-of-trace-objects

[nathan-vo810]

Unfortunately, that can only update the trace's name, which is the function name - main, but not the span's name (RunnableSequence).

I would like to update the name of the span which is created from running the chain.invoke from RunnableSequence to something else. The reason is in 1 function I call multiple chain.invoke and all of the have the same RunnableSequence name which is not very meaningful.

[nathan-vo810]

One note is when passing langfuse_handler to langchain built-in chain, the span can take the name of it. For example: ConversationalRetrievalChain or StuffDocumentChain.

The RunnableSequence appear when building chain:
chain = prompt | llm

[marcklingen]

This is how langfuse extracts the name for each trace and its observations. Feedback/improvements appreciated if there is a way to help you customize names in a more meaningful way.

https://github.com/langfuse/langfuse-python/blob/d71a3a2b347ad899d566eae0a9d1620e22c97eb8/langfuse/callback/langchain.py#L124

[nathan-vo810]

Thanks for the reference. I figured it out!

Simply assign chain.name="New name" solved the problem.

[marcklingen]

awesome!