core[major]: On Tool End Observation Casting Fix (#18798)

This PR updates the on_tool_end handlers to return the raw output from the tool instead of casting it to a string. 

This is technically a breaking change, though it's impact is expected to be somewhat minimal. It will fix behavior in `astream_events` as well.

Fixes the following issue #18760 raised by @eyurtsev

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

docs/docs/modules/agents/how_to/streaming.ipynb

@@ -1068,7 +1068,7 @@
     "\n",
     "    def on_tool_end(\n",
     "        self,\n",
-    "        output: str,\n",
+    "        output: Any,\n",
     "        *,\n",
     "        run_id: UUID,\n",
     "        parent_run_id: Optional[UUID] = None,\n",
@@ -1076,7 +1076,7 @@
     "    ) -> Any:\n",
     "        \"\"\"Run when tool ends running.\"\"\"\n",
     "        print(\"Tool end\")\n",
-    "        print(output)\n",
+    "        print(str(output))\n",
     "\n",
     "    async def on_llm_end(\n",
     "        self,\n",

docs/docs/modules/callbacks/index.mdx

@@ -59,7 +59,7 @@ class BaseCallbackHandler:
     ) -> Any:
         """Run when tool starts running."""
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> Any:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> Any:
         """Run when tool ends running."""
 
     def on_tool_error(

libs/community/langchain_community/callbacks/aim_callback.py

@@ -314,8 +314,9 @@ class AimCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
 
         self._run.track(aim.Text(input_str), name="on_tool_start", context=resp)
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         aim = import_aim()
         self.step += 1
         self.tool_ends += 1

libs/community/langchain_community/callbacks/argilla_callback.py

@@ -328,7 +328,7 @@ class ArgillaCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,

libs/community/langchain_community/callbacks/arize_callback.py

@@ -196,7 +196,7 @@ class ArizeCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,

libs/community/langchain_community/callbacks/arthur_callback.py

@@ -279,7 +279,7 @@ class ArthurCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,

libs/community/langchain_community/callbacks/clearml_callback.py

@@ -243,8 +243,9 @@ class ClearMLCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
         if self.stream_logs:
             self.logger.report_text(resp)
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         self.step += 1
         self.tool_ends += 1
         self.ends += 1

libs/community/langchain_community/callbacks/comet_ml_callback.py

@@ -303,8 +303,9 @@ class CometCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
         resp.update({"input_str": input_str})
         self.action_records.append(resp)
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         self.step += 1
         self.tool_ends += 1
         self.ends += 1

libs/community/langchain_community/callbacks/confident_callback.py

@@ -162,7 +162,7 @@ class DeepEvalCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,

libs/community/langchain_community/callbacks/llmonitor_callback.py

@@ -465,13 +465,14 @@ class LLMonitorCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         *,
         run_id: UUID,
         parent_run_id: Union[UUID, None] = None,
         tags: Union[List[str], None] = None,
         **kwargs: Any,
     ) -> None:
+        output = str(output)
         if self.__has_valid_config is False:
             return
         try:

libs/community/langchain_community/callbacks/mlflow_callback.py

@@ -518,8 +518,9 @@ class MlflowCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
         self.records["action_records"].append(resp)
         self.mlflg.jsonf(resp, f"tool_start_{tool_starts}")
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         self.metrics["step"] += 1
         self.metrics["tool_ends"] += 1
         self.metrics["ends"] += 1

libs/community/langchain_community/callbacks/sagemaker_callback.py

@@ -186,8 +186,9 @@ class SageMakerCallbackHandler(BaseCallbackHandler):
 
         self.jsonf(resp, self.temp_dir, f"tool_start_{tool_starts}")
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         self.metrics["step"] += 1
         self.metrics["tool_ends"] += 1
         self.metrics["ends"] += 1

libs/community/langchain_community/callbacks/streamlit/streamlit_callback_handler.py

@@ -183,13 +183,13 @@ class LLMThought:
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         color: Optional[str] = None,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,
     ) -> None:
-        self._container.markdown(f"**{output}**")
+        self._container.markdown(f"**{str(output)}**")
 
     def on_tool_error(self, error: BaseException, **kwargs: Any) -> None:
         self._container.markdown("**Tool encountered an error...**")
@@ -363,12 +363,13 @@ class StreamlitCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         color: Optional[str] = None,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,
     ) -> None:
+        output = str(output)
         self._require_current_thought().on_tool_end(
             output, color, observation_prefix, llm_prefix, **kwargs
         )

libs/community/langchain_community/callbacks/wandb_callback.py

@@ -356,8 +356,9 @@ class WandbCallbackHandler(BaseMetadataCallbackHandler, BaseCallbackHandler):
         if self.stream_logs:
             self.run.log(resp)
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
+        output = str(output)
         self.step += 1
         self.tool_ends += 1
         self.ends += 1

libs/core/langchain_core/callbacks/base.py

@@ -133,7 +133,7 @@ class ToolManagerMixin:
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         *,
         run_id: UUID,
         parent_run_id: Optional[UUID] = None,
@@ -440,7 +440,7 @@ class AsyncCallbackHandler(BaseCallbackHandler):
 
     async def on_tool_end(
         self,
-        output: str,
+        output: Any,
         *,
         run_id: UUID,
         parent_run_id: Optional[UUID] = None,

libs/core/langchain_core/callbacks/manager.py

@@ -976,14 +976,15 @@ class CallbackManagerForToolRun(ParentRunManager, ToolManagerMixin):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         **kwargs: Any,
     ) -> None:
         """Run when tool ends running.
 
         Args:
-            output (str): The output of the tool.
+            output (Any): The output of the tool.
         """
+        output = str(output)
         handle_event(
             self.handlers,
             "on_tool_end",
@@ -1038,12 +1039,13 @@ class AsyncCallbackManagerForToolRun(AsyncParentRunManager, ToolManagerMixin):
         )
 
     @shielded
-    async def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    async def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running.
 
         Args:
-            output (str): The output of the tool.
+            output (Any): The output of the tool.
         """
+        output = str(output)
         await ahandle_event(
             self.handlers,
             "on_tool_end",

libs/core/langchain_core/callbacks/stdout.py

@@ -37,13 +37,14 @@ class StdOutCallbackHandler(BaseCallbackHandler):
 
     def on_tool_end(
         self,
-        output: str,
+        output: Any,
         color: Optional[str] = None,
         observation_prefix: Optional[str] = None,
         llm_prefix: Optional[str] = None,
         **kwargs: Any,
     ) -> None:
         """If not the final action, print out observation."""
+        output = str(output)
         if observation_prefix is not None:
             print_text(f"\n{observation_prefix}")
         print_text(output, color=color or self.color)

libs/core/langchain_core/callbacks/streaming_stdout.py

@@ -59,7 +59,7 @@ class StreamingStdOutCallbackHandler(BaseCallbackHandler):
         """Run on agent action."""
         pass
 
-    def on_tool_end(self, output: str, **kwargs: Any) -> None:
+    def on_tool_end(self, output: Any, **kwargs: Any) -> None:
         """Run when tool ends running."""
 
     def on_tool_error(self, error: BaseException, **kwargs: Any) -> None:

libs/core/langchain_core/tools.py

@@ -410,17 +410,13 @@ class ChildTool(BaseTool):
                     f"Got unexpected type of `handle_tool_error`. Expected bool, str "
                     f"or callable. Received: {self.handle_tool_error}"
                 )
-            run_manager.on_tool_end(
-                str(observation), color="red", name=self.name, **kwargs
-            )
+            run_manager.on_tool_end(observation, color="red", name=self.name, **kwargs)
             return observation
         except (Exception, KeyboardInterrupt) as e:
             run_manager.on_tool_error(e)
             raise e
         else:
-            run_manager.on_tool_end(
-                str(observation), color=color, name=self.name, **kwargs
-            )
+            run_manager.on_tool_end(observation, color=color, name=self.name, **kwargs)
             return observation
 
     async def arun(
@@ -502,7 +498,7 @@ class ChildTool(BaseTool):
                     f"or callable. Received: {self.handle_tool_error}"
                 )
             await run_manager.on_tool_end(
-                str(observation), color="red", name=self.name, **kwargs
+                observation, color="red", name=self.name, **kwargs
             )
             return observation
         except (Exception, KeyboardInterrupt) as e:
@@ -510,7 +506,7 @@ class ChildTool(BaseTool):
             raise e
         else:
             await run_manager.on_tool_end(
-                str(observation), color=color, name=self.name, **kwargs
+                observation, color=color, name=self.name, **kwargs
             )
             return observation
 

libs/core/langchain_core/tracers/base.py

@@ -504,8 +504,9 @@ class BaseTracer(BaseCallbackHandler, ABC):
         self._on_tool_start(tool_run)
         return tool_run
 
-    def on_tool_end(self, output: str, *, run_id: UUID, **kwargs: Any) -> Run:
+    def on_tool_end(self, output: Any, *, run_id: UUID, **kwargs: Any) -> Run:
         """End a trace for a tool run."""
+        output = str(output)
         tool_run = self._get_run(run_id, run_type="tool")
         tool_run.outputs = {"output": output}
         tool_run.end_time = datetime.now(timezone.utc)