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feat(langchain): add update_trace argument #1302

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Merged
hassiebp merged 3 commits into from
Aug 19, 2025
Merged

feat(langchain): add update_trace argument #1302

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79e7fec
feat(langchain): add update_trace argument
hassiebp Aug 19, 2025
f7b064b
Update langfuse/langchain/CallbackHandler.py
hassiebp Aug 19, 2025
e96f13b
add docs
hassiebp Aug 19, 2025
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30 changes: 26 additions & 4 deletions langfuse/langchain/CallbackHandler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -56,14 +56,17 @@


class LangchainCallbackHandler(LangchainBaseCallbackHandler):
def __init__(self, *, public_key: Optional[str] = None) -> None:
def __init__(
self, *, public_key: Optional[str] = None, update_trace: Optional[bool] = False
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) -> None:
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,
Expand Down Expand Up @@ -207,7 +210,19 @@ 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:
Expand Down Expand Up @@ -322,14 +337,21 @@ 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)

Expand Down