docs: upgrade langfuse example to python sdk v3 (#31654)

As the Langfuse python sdk v3 includes breaking changes, this PR updates
the code examples.

https://langfuse.com/docs/integrations/langchain/upgrade-paths#python
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Jannik Maierhöfer 2025-06-18 19:30:39 +02:00 committed by GitHub
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@ -15,19 +15,35 @@ pip install langfuse
```
```python
# Initialize Langfuse handler
from langfuse.callback import CallbackHandler
langfuse_handler = CallbackHandler(
secret_key="sk-lf-...",
public_key="pk-lf-...",
host="https://cloud.langfuse.com", # 🇪🇺 EU region
# host="https://us.cloud.langfuse.com", # 🇺🇸 US region
from langfuse import Langfuse, get_client
from langfuse.langchain import CallbackHandler
from langchain_openai import ChatOpenAI # Example LLM
from langchain_core.prompts import ChatPromptTemplate
# Initialize Langfuse client with constructor arguments
Langfuse(
public_key="your-public-key",
secret_key="your-secret-key",
host="https://cloud.langfuse.com" # Optional: defaults to https://cloud.langfuse.com
)
# Your Langchain code
# Get the configured client instance
langfuse = get_client()
# Add Langfuse handler as callback (classic and LCEL)
chain.invoke({"input": "<user_input>"}, config={"callbacks": [langfuse_handler]})
# Initialize the Langfuse handler
langfuse_handler = CallbackHandler()
# Create your LangChain components
llm = ChatOpenAI(model_name="gpt-4o")
prompt = ChatPromptTemplate.from_template("Tell me a joke about {topic}")
chain = prompt | llm
# Run your chain with Langfuse tracing
response = chain.invoke({"topic": "cats"}, config={"callbacks": [langfuse_handler]})
print(response.content)
# Flush events to Langfuse in short-lived applications
langfuse.flush()
```
### Environment variables
@ -43,7 +59,7 @@ LANGFUSE_HOST="https://cloud.langfuse.com"
```python
# Initialize Langfuse handler
from langfuse.callback import CallbackHandler
from langfuse.langchain import CallbackHandler
langfuse_handler = CallbackHandler()
# Your Langchain code
@ -140,7 +156,7 @@ Now, we will add then [Langfuse callback handler for LangChain](https://langfuse
```python
from langfuse.callback import CallbackHandler
from langfuse.langchain import CallbackHandler
# Initialize Langfuse CallbackHandler for Langchain (tracing)
langfuse_handler = CallbackHandler()