TheAlgorithms/Python · error · ValueError

surface_area_sphere() only accepts non-negative values

Error message

surface_area_sphere() only accepts non-negative values

What it means

surface_area_sphere() raises this ValueError when radius is negative. Radius is a physical length; the library enforces radius >= 0 before returning 4 * pi * radius**2 rather than silently squaring the sign away. Note that squaring would hide the error, which is exactly why the guard exists.

Source

Thrown at maths/area.py:79

    Calculate the Surface Area of a Sphere.
    Wikipedia reference: https://en.wikipedia.org/wiki/Sphere
    Formula: 4 * pi * r^2

    >>> surface_area_sphere(5)
    314.1592653589793
    >>> surface_area_sphere(1)
    12.566370614359172
    >>> surface_area_sphere(1.6)
    32.169908772759484
    >>> surface_area_sphere(0)
    0.0
    >>> surface_area_sphere(-1)
    Traceback (most recent call last):
        ...
    ValueError: surface_area_sphere() only accepts non-negative values
    """
    if radius < 0:
        raise ValueError("surface_area_sphere() only accepts non-negative values")
    return 4 * pi * radius**2


def surface_area_hemisphere(radius: float) -> float:
    """
    Calculate the Surface Area of a Hemisphere.
    Formula: 3 * pi * r^2

    >>> surface_area_hemisphere(5)
    235.61944901923448
    >>> surface_area_hemisphere(1)
    9.42477796076938
    >>> surface_area_hemisphere(0)
    0.0
    >>> surface_area_hemisphere(1.1)
    11.40398133253095
    >>> surface_area_hemisphere(-1)
    Traceback (most recent call last):

View on GitHub (pinned to f5988cc097)

Solutions

1. Check radius >= 0 before calling and fix the upstream computation that produced a negative value.
2. Pass abs(radius) only if the sign truly is spurious and a magnitude is what you mean.
3. Restrict CLI argument types (e.g. custom argparse type that rejects negatives).
4. Wrap in try/except ValueError to surface a friendly message.

Example fix

// before
area = surface_area_sphere(r)  # r = center_x - point_x, can be negative

# after
r = abs(point_x - center_x)
area = surface_area_sphere(r)

if radius < 0:
    raise ValueError(f'sphere radius must be >= 0, got {radius}')
area = surface_area_sphere(radius)

def is_valid_radius(r: object) -> bool:
    return isinstance(r, (int, float)) and not isinstance(r, bool) and r >= 0

try:
    area = surface_area_sphere(radius)
except ValueError as e:
    raise ValueError(f'cannot compute sphere area: {e}') from e

When it happens

Trigger: Calling surface_area_sphere(radius) with radius < 0, e.g. surface_area_sphere(-1). Common when radius is computed as a difference or parsed from user text including a stray '-' sign.

Common situations: Radius derived from coordinate deltas where the direction is negative; CLI arguments parsed with argparse allowing negative numbers; data files using negative values as null markers.

Related errors

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

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/0a88fee458f276c3. Report an issue: GitHub.