feat(langchain): add update_trace argument (#1302)

Author: hassiebp

langfuse/langchain/CallbackHandler.py

@@ -56,14 +56,23 @@
 
 
 class LangchainCallbackHandler(LangchainBaseCallbackHandler):
-    def __init__(self, *, public_key: Optional[str] = None) -> None:
+    def __init__(
+        self, *, public_key: Optional[str] = None, update_trace: bool = False
+    ) -> None:
+        """Initialize the LangchainCallbackHandler.
+
+        Args:
+            public_key: Optional Langfuse public key. If not provided, will use the default client configuration.
+            update_trace: Whether to update the Langfuse trace with the chains input / output / metadata / name. Defaults to False.
+        """
         self.client = get_client(public_key=public_key)
 
         self.runs: Dict[UUID, Union[LangfuseSpan, LangfuseGeneration]] = {}
         self.prompt_to_parent_run_map: Dict[UUID, Any] = {}
         self.updated_completion_start_time_memo: Set[UUID] = set()
 
         self.last_trace_id: Optional[str] = None
+        self.update_trace = update_trace
 
     def on_llm_new_token(
         self,
@@ -207,7 +216,19 @@ def on_chain_start(
                     ),
                 )
                 span.update_trace(
-                    **self._parse_langfuse_trace_attributes_from_metadata(metadata)
+                    **(
+                        cast(
+                            Any,
+                            {
+                                "input": inputs,
+                                "name": span_name,
+                                "metadata": span_metadata,
+                            },
+                        )
+                        if self.update_trace
+                        else {}
+                    ),
+                    **self._parse_langfuse_trace_attributes_from_metadata(metadata),
                 )
                 self.runs[run_id] = span
             else:
@@ -322,14 +343,21 @@ def on_chain_end(
             if run_id not in self.runs:
                 raise Exception("run not found")
 
-            self.runs[run_id].update(
+            span = self.runs[run_id]
+            span.update(
                 output=outputs,
                 input=kwargs.get("inputs"),
-            ).end()
+            )
+
+            if parent_run_id is None and self.update_trace:
+                span.update_trace(output=outputs, input=kwargs.get("inputs"))
+
+            span.end()
 
             del self.runs[run_id]
 
             self._deregister_langfuse_prompt(run_id)
+
         except Exception as e:
             langfuse_logger.exception(e)