TheAlgorithms/Python · error · ValueError

Invalid velocity. Should be a positive number.

Error message

Invalid velocity. Should be a positive number.

What it means

Raised by the input validator in physics/horizontal_projectile_motion.py before any projectile calculation when init_velocity is negative. The library treats init_velocity as a speed magnitude combined with a launch angle (1-90 degrees), so a negative magnitude is meaningless. Note the guard is `init_velocity < 0`, so 0 is silently accepted (yielding zero distance) even though the message says 'positive'.

Source

Thrown at physics/horizontal_projectile_motion.py:45

def check_args(init_velocity: float, angle: float) -> None:
    """
    Check that the arguments are valid
    """

    # Ensure valid instance
    if not isinstance(init_velocity, (int, float)):
        raise TypeError("Invalid velocity. Should be an integer or float.")

    if not isinstance(angle, (int, float)):
        raise TypeError("Invalid angle. Should be an integer or float.")

    # Ensure valid angle
    if angle > 90 or angle < 1:
        raise ValueError("Invalid angle. Range is 1-90 degrees.")

    # Ensure valid velocity
    if init_velocity < 0:
        raise ValueError("Invalid velocity. Should be a positive number.")


def horizontal_distance(init_velocity: float, angle: float) -> float:
    r"""
    Returns the horizontal distance that the object cover

    Formula:
        .. math::
            \frac{v_0^2 \cdot \sin(2 \alpha)}{g}

            v_0 - \text{initial velocity}

            \alpha - \text{angle}

    >>> horizontal_distance(30, 45)
    91.77
    >>> horizontal_distance(100, 78)
    414.76

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass the speed magnitude (>= 0) and express direction through the angle parameter, e.g. horizontal_distance(30, 45) instead of horizontal_distance(-30, 45).
2. Pre-validate inputs with abs(init_velocity) or an explicit `if init_velocity < 0` check before calling.
3. Wrap the call in try/except ValueError to convert the message into a user-facing error.

Example fix

# before
horizontal_distance(-30, 45)  # ValueError

# after
horizontal_distance(abs(-30), 45)  # or horizontal_distance(30, 45)

def valid_projectile_inputs(v: float, angle: float) -> bool:
    return isinstance(v, (int, float)) and v >= 0 and 1 <= angle <= 90

if valid_projectile_inputs(init_velocity, angle):
    horizontal_distance(init_velocity, angle)

try:
    horizontal_distance(v, angle)
except ValueError as e:
    raise ValueError(f"Projectile input rejected: {e} (v={v}, angle={angle})") from e

When it happens

Trigger: Calling horizontal_distance(-30, 45) or any function in the module that runs this validator with a negative init_velocity. Non-numeric inputs raise TypeError first; the angle check (1-90) runs independently of this one.

Common situations: Passing a signed velocity component (e.g. modeling leftward motion as -v) instead of magnitude+angle; piping raw sensor or CSV data that encodes direction in the sign; off-by-one defaults like -1 used as an 'unset' sentinel.

Related errors

• Expected a_coeffs to have {self.order + 1} elements for {sel
• n must not be negative
• Depth cannot be less than 0
• All input parameters must be positive
• Invalid inputs. Enter positive value.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/aa277adc1e5365f3. Report an issue: GitHub.