TheAlgorithms/Python · error · ValueError

area_rectangle() only accepts non-negative values

Error message

area_rectangle() only accepts non-negative values

What it means

area_rectangle() raises this ValueError when length or width is negative. The library enforces non-negative side lengths before returning length * width. Although a negative times a negative would give a positive number, that result would be meaningless as an area, so the input is rejected up front.

Source

Thrown at maths/area.py:263

    >>> area_rectangle(1.6, 2.6)
    4.16
    >>> area_rectangle(0, 0)
    0
    >>> area_rectangle(-1, -2)
    Traceback (most recent call last):
        ...
    ValueError: area_rectangle() only accepts non-negative values
    >>> area_rectangle(1, -2)
    Traceback (most recent call last):
        ...
    ValueError: area_rectangle() only accepts non-negative values
    >>> area_rectangle(-1, 2)
    Traceback (most recent call last):
        ...
    ValueError: area_rectangle() only accepts non-negative values
    """
    if length < 0 or width < 0:
        raise ValueError("area_rectangle() only accepts non-negative values")
    return length * width


def area_square(side_length: float) -> float:
    """
    Calculate the area of a square.

    >>> area_square(10)
    100
    >>> area_square(0)
    0
    >>> area_square(1.6)
    2.5600000000000005
    >>> area_square(-1)
    Traceback (most recent call last):
        ...
    ValueError: area_square() only accepts non-negative values
    """

View on GitHub (pinned to f5988cc097)

Solutions

1. Validate length >= 0 and width >= 0 before the call; correct the sign at the source.
2. Convert signed measurements to magnitudes with abs() when direction is irrelevant.
3. Replace -1 sentinels with explicit missing-value handling during import.
4. Catch ValueError for user-facing reporting.

Example fix

// before
area = area_rectangle(l, w)  # l = x2 - x1 may be negative

# after
l, w = abs(x2 - x1), abs(y2 - y1)
area = area_rectangle(l, w)

if length < 0 or width < 0:
    raise ValueError(f'rectangle sides must be >= 0: {length}, {width}')
area = area_rectangle(length, width)

def is_valid_rect_sides(l: float, w: float) -> bool:
    return l >= 0 and w >= 0

try:
    area = area_rectangle(length, width)
except ValueError as e:
    raise ValueError(f'invalid rectangle input: {e}') from e

When it happens

Trigger: Calling area_rectangle(length, width) with length < 0 or width < 0, e.g. area_rectangle(-1, 2) or area_rectangle(1, -2).

Common situations: Room/plot dimensions from survey data with sign conventions (e.g. southward as negative); spreadsheet -1 sentinels for missing widths; differences of coordinates used directly as lengths.

Related errors

• surface_area_cube() only accepts non-negative values
• surface_area_cuboid() only accepts non-negative values
• surface_area_sphere() only accepts non-negative values
• surface_area_hemisphere() only accepts non-negative values
• surface_area_cone() only accepts non-negative values

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/42c7dfe9302da1e0. Report an issue: GitHub.