pola-rs/polars · error · ValueError

the length of ` ` ( ) does not match the length of ` ` ( )

Error message

the length of `{value_name}` ({len(values)}) does not match the length of `{match_name}` ({n_match})

What it means

extend_bool expands a scalar bool to match a length and then validates that the resulting list length equals the number of rows/keys of the match input (by/over, etc.). If the provided list's length differs from n_match, it raises ValueError stating both lengths and the parameter names. It guards sort_by/arg_sort_by/top_k-style APIs against misaligned per-row option lists.

Solutions

1. Make the list length match: descending=[True, False] for two `by` columns, or pass a scalar bool instead of a list.
2. Compute lengths programmatically: descending=[True]*len(by_cols).
3. Double-check that value_name and match_name in the message refer to the parameters you intended to align.

Example fix

// before
df.sort(['a', 'b'], descending=[True])
// after
df.sort(['a', 'b'], descending=[True, False])

assert len(descending) == len(by_cols), f'descending ({len(descending)}) != by ({len(by_cols)})'

def lengths_match(a, b) -> bool:
    return len(a) == len(b)

try:
    df.sort(by_cols, descending=descending)
except ValueError as e:
    if 'does not match the length of' in str(e):
        descending = descending * len(by_cols) if len(descending) == 1 else [False]*len(by_cols)
        df = df.sort(by_cols, descending=descending)

When it happens

Trigger: Calling sort/arg_sort_by/sort_by/top_k/top_k_by/bottom_k_by with by/over/descending/... option lists whose length doesn't equal the number of columns or rows expected, e.g. df.sort('a','b', descending=[True]) or df.top_k(k, by=['x','y'], reverse=[True]).

Common situations: Adding/removing a column in the `by`/`over` list without updating the parallel options list; passing multiple columns but a single-element list where a scalar would have been accepted.

Related errors

• expected at least one Series in 'coalesce' if 'eager=True'
• expected at least one Series in 'corr' inputs if…
• expected at least one Series in 'cov' inputs if 'eager=True'
• 'length' must be an integer, string, or expression, not
• list.to_struct() got a str instead of a list. hint: pass

AI-assisted analysis of pola-rs/polars@fe841f959e (2026-09-18). Data as JSON: /api/errors/f2da204314bf393f. Report an issue: GitHub.

Appendix: source

Thrown at py-polars/src/polars/_utils/various.py:560

        del stack_frame

    return objects


def extend_bool(
    value: bool | Sequence[bool],  # noqa: FBT001
    n_match: int,
    value_name: str,
    match_name: str,
) -> Sequence[bool]:
    """Ensure the given bool or sequence of bools is the correct length."""
    values = [value] * n_match if isinstance(value, bool) else value
    if n_match != len(values):
        msg = (
            f"the length of `{value_name}` ({len(values)}) "
            f"does not match the length of `{match_name}` ({n_match})"
        )
        raise ValueError(msg)
    return values


def in_terminal_that_supports_colour() -> bool:
    """
    Determine (within reason) if we are in an interactive terminal that supports color.

    Note: this is not exhaustive, but it covers a lot (most?) of the common cases.
    """
    if hasattr(sys.stdout, "isatty"):
        # can enhance as necessary, but this is a reasonable start
        return (
            sys.stdout.isatty()
            and (
                sys.platform != "win32"
                or "ANSICON" in os.environ
                or "WT_SESSION" in os.environ
                or os.environ.get("TERM_PROGRAM") == "vscode"

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