TheAlgorithms/Python · error · ValueError

Invalid inputs. Enter positive value.

Error message

Invalid inputs. Enter positive value.

What it means

Raised by pressure_of_gas_system(moles, kelvin, volume) when moles, kelvin, or volume is negative, since amount of substance, absolute temperature, and volume are physically non-negative. It computes P = nRT/V. Note zero volume is NOT caught here and will raise ZeroDivisionError instead.

Source

Thrown at physics/ideal_gas_law.py:36

(Description adapted from https://en.wikipedia.org/wiki/Ideal_gas_law )
"""

UNIVERSAL_GAS_CONSTANT = 8.314462  # Unit - J mol-1 K-1


def pressure_of_gas_system(moles: float, kelvin: float, volume: float) -> float:
    """
    >>> pressure_of_gas_system(2, 100, 5)
    332.57848
    >>> pressure_of_gas_system(0.5, 273, 0.004)
    283731.01575
    >>> pressure_of_gas_system(3, -0.46, 23.5)
    Traceback (most recent call last):
        ...
    ValueError: Invalid inputs. Enter positive value.
    """
    if moles < 0 or kelvin < 0 or volume < 0:
        raise ValueError("Invalid inputs. Enter positive value.")
    return moles * kelvin * UNIVERSAL_GAS_CONSTANT / volume


def volume_of_gas_system(moles: float, kelvin: float, pressure: float) -> float:
    """
    >>> volume_of_gas_system(2, 100, 5)
    332.57848
    >>> volume_of_gas_system(0.5, 273, 0.004)
    283731.01575
    >>> volume_of_gas_system(3, -0.46, 23.5)
    Traceback (most recent call last):
        ...
    ValueError: Invalid inputs. Enter positive value.
    """
    if moles < 0 or kelvin < 0 or pressure < 0:
        raise ValueError("Invalid inputs. Enter positive value.")
    return moles * kelvin * UNIVERSAL_GAS_CONSTANT / pressure

View on GitHub (pinned to f5988cc097)

Solutions

1. Convert temperatures to kelvin (add 273.15 to Celsius) before calling.
2. Sanitize inputs: reject or clamp negative moles/kelvin/volume before the call.
3. Also guard volume == 0 yourself, since the library only checks < 0 and zero causes ZeroDivisionError.

Example fix

# before
pressure_of_gas_system(3, -46, 23.5)  # ValueError

# after
pressure_of_gas_system(3, 273.15 - 46, 23.5)  # Celsius -> kelvin

def valid_gas_inputs(*vals: float) -> bool:
    return all(v > 0 for v in vals)  # strictly positive also avoids the 0-volume ZeroDivisionError

if valid_gas_inputs(moles, kelvin, volume):
    pressure_of_gas_system(moles, kelvin, volume)

try:
    pressure_of_gas_system(n, t, v)
except ValueError:
    print('moles, kelvin, and volume must be non-negative')
except ZeroDivisionError:
    print('volume must also be non-zero')

When it happens

Trigger: pressure_of_gas_system(3, -0.46, 23.5) from the doctest; any call with a negative temperature in Celsius-style values (e.g. -20) fed directly as kelvin.

Common situations: Feeding Celsius temperatures into a parameter that expects kelvin; negative volumes from upstream subtraction bugs; unit-conversion mistakes between m^3 and liters producing sign or scale errors.

Related errors

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

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/bc8906b0e87cee53. Report an issue: GitHub.