langchain-ai/langgraph · error · TypeError

Object of type {obj.__class__.__name__} is not serializable

Error message

Object of type {obj.__class__.__name__} is not serializable

What it means

Error "Object of type {obj.__class__.__name__} is not serializable" thrown in langchain-ai/langgraph.

Source

Thrown at libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py:534

        obj, np_mod.ndarray
    ):
        order = "F" if obj.flags.f_contiguous and not obj.flags.c_contiguous else "C"
        if obj.flags.c_contiguous:
            mv = memoryview(obj)
            try:
                meta = (obj.dtype.str, obj.shape, order, mv)
                return ormsgpack.Ext(EXT_NUMPY_ARRAY, _msgpack_enc(meta))
            finally:
                mv.release()
        else:
            buf = obj.tobytes(order="A")
            meta = (obj.dtype.str, obj.shape, order, buf)
            return ormsgpack.Ext(EXT_NUMPY_ARRAY, _msgpack_enc(meta))

    elif isinstance(obj, BaseException):
        return repr(obj)
    else:
        raise TypeError(f"Object of type {obj.__class__.__name__} is not serializable")


def _send_from_args(args: Sequence[Any]) -> Any:
    # ya we have a cyclic import here ¯\_(ツ)_/¯
    from langgraph.types import Send  # type: ignore

    if len(args) == 2:
        return Send(*args)
    return Send(args[0], args[1], timeout=args[2])


def _create_msgpack_ext_hook(
    allowed_modules: set[tuple[str, ...]] | Literal[True] | None,
) -> Callable[[int, bytes], Any]:
    """Create msgpack ext hook with allowlist.

    Args:
        allowed_modules: Set of (module, name) tuples that are allowed to be

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py:534 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/ec89b3fe92636a50. Report an issue: GitHub.