lancedb/lancedb · error · ValueError

Cannot add note to exception

Error message

Cannot add note to exception

What it means

add_note attaches a note to an exception either via the Python 3.11+ add_note method, or by string-concatenating onto args[0] if args[0] is a str. If the base exception's first arg is not a string and add_note is unavailable, it raises ValueError('Cannot add note to exception').

Solutions

1. Upgrade to Python 3.11+ where native add_note is always used
2. Before calling, ensure the target exception has a string first arg, or re-wrap it: raise type(exc)(str(exc)) from exc
3. Wrap the original exception in a RuntimeError with the note instead of mutating it

Example fix

// before
add_note(exc, "embedding setup failed")  # ValueError if exc.args[0] not str
// after
if not (hasattr(exc, "add_note") or (exc.args and isinstance(exc.args[0], str))):
    exc = RuntimeError(str(exc))
add_note(exc, "embedding setup failed")

def can_annotate(exc) -> bool:
    return hasattr(exc, "add_note") or bool(exc.args and isinstance(exc.args[0], str))

def annotatable(exc: BaseException) -> bool:
    return hasattr(exc, "add_note") or (exc.args and isinstance(exc.args[0], str))

try:
    add_note(exc, note)
except ValueError as e:
    if "Cannot add note" in str(e):
        raise RuntimeError(f"{note}: {exc!r}") from exc
    raise

When it happens

Trigger: Calling add_note(exc, note) (directly or via _add_unique_note in the embedding error path, e.g. __resolveVariables/get_embedding_func failures) on an exception whose args[0] is not a str (e.g. KeyError with non-string key, custom exception taking an int) on Python < 3.11.

Common situations: Annotating exceptions raised by libraries that pass non-string payloads (KeyError('missing_col') actually has str args, but KeyError(404) does not); running on Python 3.10 or older where Exception.add_note does not exist.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• a Function environment is pip or conda, not both
• add_columns cannot mix a Function application with SQL…
• add_columns cannot take both transforms and computed columns
• add_columns requires transforms or computed columns
• All datasets in a HuggingFace DatasetDict must have the…

AI-assisted analysis of lancedb/lancedb@c7b051aff7 (2026-09-08). Data as JSON: /api/errors/cda23e8d42ac5cb2. Report an issue: GitHub.

Appendix: source

Thrown at python/python/lancedb/util.py:459

    return new_func


def validate_table_name(name: str):
    """Verify the table name is valid."""
    native_validate_table_name(name)


def add_note(base_exception: BaseException, note: str):
    if hasattr(base_exception, "add_note"):
        base_exception.add_note(note)
    elif isinstance(base_exception.args[0], str):
        base_exception.args = (
            base_exception.args[0] + "\n" + note,
            *base_exception.args[1:],
        )
    else:
        raise ValueError("Cannot add note to exception")


def tbl_to_tensor(tbl: pa.Table):
    """
    Convert a PyArrow Table to a PyTorch Tensor.

    Each column is converted to a tensor (using zero-copy via DLPack)
    and the columns are then stacked into a single tensor.

    Fails if torch is not installed.
    Fails if any column is more than one chunk.
    Fails if a column's data type is not supported by PyTorch.

    Parameters
    ----------
    tbl : pa.Table or pa.RecordBatch
        The table or record batch to convert to a tensor.

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