langchain-ai/langgraph · error · ValueError

At least one of func or afunc must be provided.

Error message

At least one of func or afunc must be provided.

What it means

Error "At least one of func or afunc must be provided." thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/_internal/_runnable.py:336

                    if func.__name__ != "<lambda>":
                        self.name = func.__name__
                except AttributeError:
                    pass
            elif afunc:
                try:
                    self.name = afunc.__name__
                except AttributeError:
                    pass
        self.func = func
        self.afunc = afunc
        self.tags = tags
        self.kwargs = kwargs
        self.trace = trace
        self.recurse = recurse
        self.explode_args = explode_args
        # check signature
        if func is None and afunc is None:
            raise ValueError("At least one of func or afunc must be provided.")

        self.func_accepts: dict[str, tuple[str, Any]] = {}
        params = inspect.signature(cast(Callable, func or afunc)).parameters

        for kw, typ, runtime_key, default in KWARGS_CONFIG_KEYS:
            p = params.get(kw)

            if p is None or p.kind not in VALID_KINDS:
                # If parameter is not found or is not a valid kind, skip
                continue

            if typ != (ANY_TYPE,) and p.annotation not in typ:
                # A specific type is required, but the function annotation does
                # not match the expected type.

                # If this is a config parameter with incorrect typing, emit a warning
                # because we used to support any type but are moving towards more correct typing
                if kw == "config" and p.annotation != inspect.Parameter.empty:

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/_internal/_runnable.py:336 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/caafc61536a92870. Report an issue: GitHub.