don't update events

Author: nimarb

langfuse/_client/span.py

@@ -1570,6 +1570,36 @@ def __init__(
             status_message=status_message,
         )
 
+    def update(
+        self,
+        *,
+        name: Optional[str] = None,
+        input: Optional[Any] = None,
+        output: Optional[Any] = None,
+        metadata: Optional[Any] = None,
+        version: Optional[str] = None,
+        level: Optional[SpanLevel] = None,
+        status_message: Optional[str] = None,
+        completion_start_time: Optional[datetime] = None,
+        model: Optional[str] = None,
+        model_parameters: Optional[Dict[str, MapValue]] = None,
+        usage_details: Optional[Dict[str, int]] = None,
+        cost_details: Optional[Dict[str, float]] = None,
+        prompt: Optional[PromptClient] = None,
+        **kwargs: Any,
+    ) -> "LangfuseObservationWrapper":
+        """Update is not allowed for LangfuseEvent because events cannot be updated.
+
+        This method logs a warning and returns self without making changes.
+
+        Returns:
+            self: Returns the unchanged LangfuseEvent instance
+        """
+        langfuse_logger.warning(
+            "Attempted to update LangfuseEvent observation. Events cannot be updated after creation."
+        )
+        return self
+
 
 class LangfuseAgent(LangfuseObservationWrapper):
     """Specialized span for agent observations in agentic workflows."""

tests/test_otel.py

@@ -628,12 +628,6 @@ def test_start_as_current_observation_types(self, langfuse_client, memory_export
                 LangfuseOtelSpanAttributes.OBSERVATION_TYPE
             )
 
-            # Debug: print all attributes for this span
-            print(
-                f"Span {expected_name} attributes: {list(span_data['attributes'].keys())}"
-            )
-            print(f"Expected: {expected_otel_type}, Actual: {actual_type}")
-
             assert (
                 actual_type == expected_otel_type
             ), f"Expected observation type {expected_otel_type}, got {actual_type}"
@@ -3036,3 +3030,33 @@ def test_different_seeds_produce_different_ids(self, langfuse_client):
 
         # All observation IDs should be unique
         assert len(set(observation_ids)) == len(seeds)
+
+    def test_langfuse_event_update_immutability(self, langfuse_client, memory_exporter, caplog):
+        """Test that LangfuseEvent.update() logs a warning and does nothing."""
+        import logging
+
+        parent_span = langfuse_client.start_span(name="parent-span")
+
+        event = parent_span.start_observation(
+            name="test-event",
+            as_type="event",
+            input={"original": "input"},
+        )
+
+        # Try to update the event and capture warning logs
+        with caplog.at_level(logging.WARNING, logger='langfuse._client.span'):
+            result = event.update(
+                name="updated_name",
+                input={"updated": "input"},
+                output={"updated": "output"},
+                metadata={"updated": "metadata"}
+            )
+
+            # Verify warning was logged
+            assert "Attempted to update LangfuseEvent observation" in caplog.text
+            assert "Events are immutable and cannot be updated after creation" in caplog.text
+
+            # Verify the method returned self unchanged
+            assert result is event
+
+        parent_span.end()