langfuse

For Langfuse SDK v3, import the `CallbackHandler` from `langfuse.langchain`. Ensure `langfuse` version 3.x is installed (e.g., `pip install 'langfuse>=3.0.0'`).

```python
# Correct for Langfuse v3
from langfuse.langchain import CallbackHandler
```

Import the `observe` decorator directly from the `langfuse` package.

```python
# Correct for Langfuse v3
from langfuse import observe

@observe()
def my_function():
    pass
```

Instead of `langfuse.trace(...)`, use the `@observe` decorator for functions or `langfuse.start_as_current_span()` (preferably with a `with` statement) for manual span management.

```python
# Correct for Langfuse v3 using decorator
from langfuse import observe

@observe(name="my-trace-name")
def my_traced_function():
    pass

# Correct for Langfuse v3 using context manager
from langfuse import get_client

langfuse = get_client()
with langfuse.start_as_current_span(name="my-span") as span:
    span.update(input="some_input")
```

Remove deprecated arguments like `sdk_integration` from the `Langfuse` constructor. Initialize the client with valid v3 arguments, such as `public_key`, `secret_key`, `host`, `debug`, or `tracing_enabled`. The recommended approach is often to use `get_client()` which relies on environment variables.

```python
# Incorrect (v2 pattern)
# langfuse = Langfuse(sdk_integration="my-app")

# Correct for Langfuse v3
from langfuse import Langfuse, get_client

# Option 1: Initialize with environment variables (recommended)
langfuse_client = get_client()

# Option 2: Initialize with constructor arguments
langfuse_client = Langfuse(
    public_key="pk-lf-...",
    secret_key="sk-lf-...",
    host="https://cloud.langfuse.com"
)
```

Ensure that `LANGFUSE_PUBLIC_KEY` and `LANGFUSE_SECRET_KEY` are set as environment variables or passed directly to the `Langfuse` client constructor. If you intend to disable tracing, ensure it's done correctly, typically by setting `tracing_enabled=False` during client initialization, or by setting `LANGFUSE_TRACING_ENABLED=false` or `OTEL_SDK_DISABLED=true` environment variables, while still providing dummy keys if needed for initialization.

```python
import os
from langfuse import Langfuse

# Ensure environment variables are set:
# os.environ["LANGFUSE_PUBLIC_KEY"] = "pk-lf-..."
# os.environ["LANGFUSE_SECRET_KEY"] = "sk-lf-..."
# os.environ["LANGFUSE_BASE_URL"] = "https://cloud.langfuse.com"

# Or pass them directly:
langfuse = Langfuse(
    public_key=os.getenv("LANGFUSE_PUBLIC_KEY", "dummy-public-key"),
    secret_key=os.getenv("LANGFUSE_SECRET_KEY", "dummy-secret-key"),
    host=os.getenv("LANGFUSE_BASE_URL", "http://localhost:3000"),
    # If tracing is explicitly disabled, ensure keys are still provided for proper initialization
    # tracing_enabled=False 
)
```