From 640d241bcafdcc6112478dc98a7a252d4d4a616b Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Thu, 16 Oct 2025 07:18:21 +0000
Subject: [PATCH] Fix #3715: Remove unwanted LLM stream chunk printing to
 stdout
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- Removed print() statement in event_listener.py that was printing all LLM streaming chunks to stdout
- The print() on line 386 was causing all text chunks from LLM responses to be displayed in stdout
- Added test to verify stream chunks are emitted as events but not printed to stdout
- Streaming chunks should only be handled by event handlers, not printed directly

Fixes #3715

Co-Authored-By: João <joao@crewai.com>
---
 src/crewai/events/event_listener.py |  1 -
 tests/utilities/test_events.py      | 36 +++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/crewai/events/event_listener.py b/src/crewai/events/event_listener.py
index a0b113f35..0aa29bce1 100644
--- a/src/crewai/events/event_listener.py
+++ b/src/crewai/events/event_listener.py
@@ -383,7 +383,6 @@ class EventListener(BaseEventListener):
 
             # Read from the in-memory stream
             content = self.text_stream.read()
-            print(content, end="", flush=True)
             self.next_chunk = self.text_stream.tell()
 
         # ----------- LLM GUARDRAIL EVENTS -----------
diff --git a/tests/utilities/test_events.py b/tests/utilities/test_events.py
index 505504c8e..09c514039 100644
--- a/tests/utilities/test_events.py
+++ b/tests/utilities/test_events.py
@@ -991,3 +991,39 @@ def test_llm_emits_event_with_lite_agent():
 
     assert set(all_agent_roles) == {agent.role}
     assert set(all_agent_id) == {agent.id}
+
+def test_llm_stream_chunks_do_not_print_to_stdout(capsys):
+    """Test that LLM streaming chunks are not printed to stdout.
+    
+    This test verifies the fix for issue #3715 where LLM stream chunks
+    were being printed directly to stdout via print() statement.
+    """
+    received_chunks = []
+
+    with crewai_event_bus.scoped_handlers():
+
+        @crewai_event_bus.on(LLMStreamChunkEvent)
+        def handle_stream_chunk(source, event):
+            received_chunks.append(event.chunk)
+
+        # Manually emit stream chunk events to simulate streaming
+        llm = LLM(model="gpt-4o", stream=True)
+        
+        test_chunks = ["Hello", " ", "world", "!"]
+        for chunk in test_chunks:
+            crewai_event_bus.emit(llm, event=LLMStreamChunkEvent(chunk=chunk))
+
+        # Capture stdout
+        captured = capsys.readouterr()
+
+        # Verify that we received chunks
+        assert len(received_chunks) == len(test_chunks), "Should receive all streaming chunks"
+        assert received_chunks == test_chunks, "Chunks should match what was emitted"
+
+        # Verify that chunks were NOT printed to stdout
+        # The bug was that all chunks were being printed via print()
+        for chunk in test_chunks:
+            assert chunk not in captured.out, (
+                f"Chunk '{chunk}' should not be printed to stdout. "
+                "This indicates the bug in event_listener.py is not fixed."
+            )