langchain-ai/langgraph · error · ValueError

types.Handler already set for {r}, {a}.

Error message

types.Handler already set for {r}, {a}.

What it means

Error "types.Handler already set for {r}, {a}." thrown in langchain-ai/langgraph.

Source

Thrown at libs/sdk-py/langgraph_sdk/auth/__init__.py:833

def _register_handler(
    auth: Auth,
    resource: str | None,
    action: str | None,
    fn: types.Handler,
) -> types.Handler:
    _validate_handler(fn)
    resource = resource or "*"
    action = action or "*"
    if resource == "*" and action == "*":
        if auth._global_handlers:
            raise ValueError("Global handler already set.")
        auth._global_handlers.append(fn)
    else:
        r = resource if resource is not None else "*"
        a = action if action is not None else "*"
        if (r, a) in auth._handlers:
            raise ValueError(f"types.Handler already set for {r}, {a}.")
        auth._handlers[(r, a)] = [fn]
    return fn


def _validate_handler(fn: Callable[..., typing.Any]) -> None:
    """Validates that an auth handler function meets the required signature.

    Auth handlers must:
    1. Be async functions
    2. Accept a ctx parameter of type AuthContext
    3. Accept a value parameter for the data being authorized
    """
    if not inspect.iscoroutinefunction(fn):
        raise ValueError(
            f"Auth handler '{getattr(fn, '__name__', fn)}' must be an async function. "
            "Add 'async' before 'def' to make it asynchronous and ensure"
            " any IO operations are non-blocking."
        )

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/auth/__init__.py:833 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/03f5a92642b4d189. Report an issue: GitHub.