Using member functions of a class as LangGraph tools

penguin_pam

I'm writing an agent using the LangChain and LangGraph libraries. I want to make my agent able to interact with files but only inside of the local directory, so I am writing a family of tools that are actually member functions of a class instance for storing the location of the local directory (which can be later expanded to have tracing/rollback functionality). The structure is as such: class FileInterface: def __init__(self): self.localdir =...

Originally asked by FLKR on Stack Exchange (stackoverflow) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

You get that error because @tool on a bound instance method is not supported. When you decorate a method like: @tool def read_file(self, path: str) -> str: ... LangChain wraps it as a StructuredTool , but since it’s already bound (i.e. self is already attached), at runtime it gets passed another implicit self → so Python sees two self args → and thus: TypeError: StructuredTool._run() got multiple values for argument 'self' In a nutshell: tools need to be plain callables, not bound methods . So, To fix this you can wrap the instance method into a closure that captures self : class FileInterface: def __init__(self, base_dir: str): self.base_dir = Path(base_dir) def _read_file(self, filename:...

Full answer by Ajeet Verma: https://stackoverflow.stackexchange.com/a/79808579 (CC BY-SA 4.0).

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