Fix intervention handler none check (#4351)

* Fix none check

* fix func

* fmt, lint

---------

Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>

python/packages/autogen-core/src/autogen_core/application/_single_threaded_agent_runtime.py

@@ -147,6 +147,23 @@ class RunContext:
         return self._run_state == RunContext.RunState.UNTIL_IDLE and self._runtime.idle
 
 
+def _warn_if_none(value: Any, handler_name: str) -> None:
+    """
+    Utility function to check if the intervention handler returned None and issue a warning.
+
+    Args:
+        value: The return value to check
+        handler_name: Name of the intervention handler method for the warning message
+    """
+    if value is None:
+        warnings.warn(
+            f"Intervention handler {handler_name} returned None. This might be unintentional. "
+            "Consider returning the original message or DropMessage explicitly.",
+            RuntimeWarning,
+            stacklevel=2,
+        )
+
+
 class SingleThreadedAgentRuntime(AgentRuntime):
     def __init__(
         self,
@@ -433,6 +450,7 @@ class SingleThreadedAgentRuntime(AgentRuntime):
                         ):
                             try:
                                 temp_message = await handler.on_send(message, sender=sender, recipient=recipient)
+                                _warn_if_none(temp_message, "on_send")
                             except BaseException as e:
                                 future.set_exception(e)
                                 return
@@ -456,6 +474,7 @@ class SingleThreadedAgentRuntime(AgentRuntime):
                         ):
                             try:
                                 temp_message = await handler.on_publish(message, sender=sender)
+                                _warn_if_none(temp_message, "on_publish")
                             except BaseException as e:
                                 # TODO: we should raise the intervention exception to the publisher.
                                 logger.error(f"Exception raised in in intervention handler: {e}", exc_info=True)
@@ -474,6 +493,7 @@ class SingleThreadedAgentRuntime(AgentRuntime):
                     for handler in self._intervention_handlers:
                         try:
                             temp_message = await handler.on_response(message, sender=sender, recipient=recipient)
+                            _warn_if_none(temp_message, "on_response")
                         except BaseException as e:
                             # TODO: should we raise the exception to sender of the response instead?
                             future.set_exception(e)

python/packages/autogen-core/src/autogen_core/base/intervention.py

@@ -1,4 +1,3 @@
-import warnings
 from typing import Any, Awaitable, Callable, Protocol, final
 
 from autogen_core.base import AgentId
@@ -15,27 +14,15 @@ __all__ = [
 class DropMessage: ...
 
 
-def _warn_if_none(value: Any, handler_name: str) -> None:
-    """
-    Utility function to check if the intervention handler returned None and issue a warning.
-
-    Args:
-        value: The return value to check
-        handler_name: Name of the intervention handler method for the warning message
-    """
-    if value is None:
-        warnings.warn(
-            f"Intervention handler {handler_name} returned None. This might be unintentional. "
-            "Consider returning the original message or DropMessage explicitly.",
-            RuntimeWarning,
-            stacklevel=2,
-        )
-
-
 InterventionFunction = Callable[[Any], Any | Awaitable[type[DropMessage]]]
 
 
 class InterventionHandler(Protocol):
+    """An intervention handler is a class that can be used to modify, log or drop messages that are being processed by the :class:`autogen_core.base.AgentRuntime`.
+
+    Note: Returning None from any of the intervention handler methods will result in a warning being issued and treated as "no change". If you intend to drop a message, you should return :class:`DropMessage` explicitly.
+    """
+
     async def on_send(self, message: Any, *, sender: AgentId | None, recipient: AgentId) -> Any | type[DropMessage]: ...
     async def on_publish(self, message: Any, *, sender: AgentId | None) -> Any | type[DropMessage]: ...
     async def on_response(
@@ -44,14 +31,15 @@ class InterventionHandler(Protocol):
 
 
 class DefaultInterventionHandler(InterventionHandler):
+    """Simple class that provides a default implementation for all intervention
+    handler methods, that simply returns the message unchanged. Allows for easy
+    subclassing to override only the desired methods."""
+
     async def on_send(self, message: Any, *, sender: AgentId | None, recipient: AgentId) -> Any | type[DropMessage]:
-        _warn_if_none(message, "on_send")
         return message
 
     async def on_publish(self, message: Any, *, sender: AgentId | None) -> Any | type[DropMessage]:
-        _warn_if_none(message, "on_publish")
         return message
 
     async def on_response(self, message: Any, *, sender: AgentId, recipient: AgentId | None) -> Any | type[DropMessage]:
-        _warn_if_none(message, "on_response")
         return message

python/packages/autogen-core/tests/test_tools.py

@@ -2,12 +2,10 @@ import inspect
 from typing import Annotated, List
 
 import pytest
-
 from autogen_core.base import CancellationToken
 from autogen_core.components._function_utils import get_typed_signature
 from autogen_core.components.tools import BaseTool, FunctionTool
 from autogen_core.components.tools._base import ToolSchema
-
 from pydantic import BaseModel, Field, model_serializer
 from pydantic_core import PydanticUndefined