🐛 Bug Report: TypeError: 'ToolNode' object is not iterable in patch.py when using langgraph-supervisor with create_react_agent

[soumen-eric]

Which component is this bug for?

Langchain Instrumentation

📜 Description

opentelemetry-instrumentation-langchain v0.53.x crashes when langgraph-supervisor's create_supervisor() passes a ToolNode object to
create_react_agent. The instrumentation's monkey-patch in patch.py (line 489) assumes tools is always an iterable list, but ToolNode is not
iterable.

Environment:

• opentelemetry-instrumentation-langchain: 0.53.3
• langgraph-prebuilt: 1.0.8
• langgraph-supervisor: latest
• Python: 3.13

👟 Reproduction steps

1. Install opentelemetry-instrumentation-langchain==0.53.3 with langgraph-supervisor
2. Create a supervisor using create_supervisor() which internally calls create_react_agent with a ToolNode object
3. Application crashes on startup

Error:
File "/usr/local/lib/python3.13/site-packages/opentelemetry/instrumentation/langchain/patch.py", line 489, in wrapper
for tool in tools:
^^^^^
TypeError: 'ToolNode' object is not iterable

👍 Expected behavior

Should work

👎 Actual Behavior with Screenshots

NA

🤖 Python Version

3.13

📃 Provide any additional context for the Bug.

Root Cause:

In patch.py lines 484-492:
python
tools = kwargs.get("tools")
if tools is None and len(args) > 1:
tools = args[1]
if tools:
tool_definitions = []
for tool in tools: # <-- ToolNode is not iterable
tool_def = _extract_tool_definition(tool)

ToolNode is a LangGraph class that wraps tools but is not itself iterable. It exposes tools via tools_by_name attribute.

Suggested Fix:

python
if tools:
tool_definitions = []
_tools_iter = tools.tools_by_name.values() if hasattr(tools, 'tools_by_name') else tools
for tool in _tools_iter:

Workaround: Pin to opentelemetry-instrumentation-langchain==0.52.6

👀 Have you spent some time to check if this bug has been raised before?

• I checked and didn't find similar issue

Are you willing to submit PR?

None

[SanjanaB123]

I'd like to work on this if its available!

[SanjanaB123]

Opened a fix for this: #3846

[JiwaniZakir]

The root cause is in patch.py around line 489, where the instrumentation assumes tools is always a list-like iterable, but ToolNode is a LangGraph graph node class that wraps tools internally rather than exposing them via direct iteration. The TypeError: 'ToolNode' object is not iterable confirms the patched create_react_agent wrapper is receiving a ToolNode instance and attempting to loop over it directly. The suggested fix using tools.tools_by_name.values() is the right approach — ToolNode stores its wrapped tools in that dict, so a hasattr guard to branch between ToolNode and a plain iterable handles both cases cleanly. Worth also checking whether other node types in LangGraph (e.g., ToolExecutor) have a similar mismatch, since this pattern of passing a pre-built node instead of a raw tools list may appear elsewhere.