langgraph: bring back tool content stringify (#1114)

libs/langgraph/langgraph/prebuilt/tool_node.py

@@ -1,4 +1,5 @@
 import asyncio
+import json
 from copy import copy
 from typing import (
     Any,
@@ -28,6 +29,16 @@
 TOOL_CALL_ERROR_TEMPLATE = "Error: {error}\n Please fix your mistakes."
 
 
+def str_output(output: Any) -> str:
+    if isinstance(output, str):
+        return output
+    else:
+        try:
+            return json.dumps(output)
+        except Exception:
+            return str(output)
+
+
 class ToolNode(RunnableCallable):
     """A node that runs the tools called in the last AIMessage.
 
@@ -94,7 +105,12 @@ def _run_one(self, call: ToolCall, config: RunnableConfig) -> ToolMessage:
 
         try:
             input = {**call, **{"type": "tool_call"}}
-            return self.tools_by_name[call["name"]].invoke(input, config)
+            tool_message: ToolMessage = self.tools_by_name[call["name"]].invoke(
+                input, config
+            )
+            # TODO: handle this properly in core
+            tool_message.content = str_output(tool_message.content)
+            return tool_message
         except Exception as e:
             if not self.handle_tool_errors:
                 raise e
@@ -106,7 +122,12 @@ async def _arun_one(self, call: ToolCall, config: RunnableConfig) -> ToolMessage
             return invalid_tool_message
         try:
             input = {**call, **{"type": "tool_call"}}
-            return await self.tools_by_name[call["name"]].ainvoke(input, config)
+            tool_message: ToolMessage = await self.tools_by_name[call["name"]].ainvoke(
+                input, config
+            )
+            # TODO: handle this properly in core
+            tool_message.content = str_output(tool_message.content)
+            return tool_message
         except Exception as e:
             if not self.handle_tool_errors:
                 raise e

libs/langgraph/tests/test_prebuilt.py

@@ -267,6 +267,13 @@ async def tool2(some_val: int, some_other_val: str) -> str:
             raise ValueError("Test error")
         return f"tool2: {some_val} - {some_other_val}"
 
+    async def tool3(some_val: int, some_other_val: str) -> str:
+        """Tool 3 docstring."""
+        return [
+            {"key_1": some_val, "key_2": "foo"},
+            {"key_1": some_other_val, "key_2": "baz"},
+        ]
+
     result = ToolNode([tool1]).invoke(
         {
             "messages": [
@@ -377,6 +384,31 @@ async def tool2(some_val: int, some_other_val: str) -> str:
     )
     assert tool_message.tool_call_id == "some 0"
 
+    # list of dicts tool content
+    result3 = await ToolNode([tool3]).ainvoke(
+        {
+            "messages": [
+                AIMessage(
+                    "hi?",
+                    tool_calls=[
+                        {
+                            "name": "tool3",
+                            "args": {"some_val": 2, "some_other_val": "bar"},
+                            "id": "some 0",
+                        }
+                    ],
+                )
+            ]
+        }
+    )
+    tool_message: ToolMessage = result3["messages"][-1]
+    assert tool_message.type == "tool"
+    assert (
+        tool_message.content
+        == '[{"key_1": 2, "key_2": "foo"}, {"key_1": "bar", "key_2": "baz"}]'
+    )
+    assert tool_message.tool_call_id == "some 0"
+
 
 def my_function(some_val: int, some_other_val: str) -> str:
     return f"{some_val} - {some_other_val}"