docs: add deprecation warning to legacy callback handler methods (#775)

langfuse/callback/langchain.py

@@ -1,6 +1,7 @@
 import httpx
 import logging
 import typing
+import warnings
 
 import pydantic
 
@@ -110,6 +111,10 @@ def __init__(
             self.runs[stateful_client.id] = stateful_client
 
     def setNextSpan(self, id: str):
+        warnings.warn(
+            "setNextSpan is deprecated, use span.get_langchain_handler() instead",
+            DeprecationWarning,
+        )
         self.next_span_id = id
 
     def on_llm_new_token(

langfuse/utils/base_callback_handler.py

@@ -2,6 +2,7 @@
 import httpx
 import logging
 import os
+import warnings
 
 from langfuse.client import Langfuse, StatefulTraceClient, StatefulSpanClient, StateType
 
@@ -110,6 +111,10 @@ def get_trace_id(self):
         Returns:
             The ID of the current/last trace or None if no trace is available.
         """
+        warnings.warn(
+            "get_trace_id is deprecated, create a trace for this handler instead. See interop documentation of this integration for more information.",
+            DeprecationWarning,
+        )
         return self.trace.id if self.trace else None
 
     def get_trace_url(self):
@@ -119,6 +124,10 @@ def get_trace_url(self):
         Returns:
             The URL of the current/last trace or None if no trace is available.
         """
+        warnings.warn(
+            "get_trace_url is deprecated, create a trace for this handler instead. See interop documentation of this integration for more information.",
+            DeprecationWarning,
+        )
         return self.trace.get_trace_url() if self.trace else None
 
     def flush(self):