TheAlgorithms/Python · error · ValueError

Exactly one argument must be 0

Error message

Exactly one argument must be 0

What it means

Thrown by electric_power() in electronics/electric_power.py when the number of zeros among (voltage, current, power) is not exactly 1. The function solves P = V*I for the single unknown, signaled by passing 0 for that argument; zero for none or for two arguments is ambiguous and rejected. Returns a Result(name, value) namedtuple.

Source

Thrown at electronics/electric_power.py:41

    >>> electric_power(voltage=2, current=4, power=2)
    Traceback (most recent call last):
        ...
    ValueError: Exactly one argument must be 0
    >>> electric_power(voltage=0, current=0, power=2)
    Traceback (most recent call last):
        ...
    ValueError: Exactly one argument must be 0
    >>> electric_power(voltage=0, current=2, power=-4)
    Traceback (most recent call last):
        ...
    ValueError: Power cannot be negative in any electrical/electronics system
    >>> electric_power(voltage=2.2, current=2.2, power=0)
    Result(name='power', value=4.84)
    >>> electric_power(current=0, power=6, voltage=2)
    Result(name='current', value=3.0)
    """
    if (voltage, current, power).count(0) != 1:
        raise ValueError("Exactly one argument must be 0")
    elif power < 0:
        raise ValueError(
            "Power cannot be negative in any electrical/electronics system"
        )
    elif voltage == 0:
        return Result("voltage", power / current)
    elif current == 0:
        return Result("current", power / voltage)
    elif power == 0:
        return Result("power", float(round(abs(voltage * current), 2)))
    else:
        raise AssertionError


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass exactly one argument as 0 — the quantity to compute — and non-zero values for the other two.
2. Remember power is computed as abs(voltage * current); the API does not encode load direction.
3. Use keyword arguments so the unknown is obvious at the call site.

Example fix

# before
electric_power(voltage=2.2, current=2.2, power=4.84)  # all supplied

# after
electric_power(voltage=2.2, current=2.2, power=0)  # -> Result(name='power', value=4.84)

args = (voltage, current, power)
if args.count(0) != 1:
    raise ValueError("pass exactly one 0 as the unknown")
result = electric_power(*args)  # Result(name='power'|'voltage'|'current', value=...)

When it happens

Trigger: electric_power(voltage=2.2, current=2.2, power=4.84) (no zero — all supplied) or electric_power(voltage=0, current=0, power=6) (two zeros). Contrast: electric_power(voltage=2.2, current=2.2, power=0) works and returns Result(name='power', value=4.84).

Common situations: New callers assuming a 3-required-argument API; treating 0W as a physical 'no power' query instead of the 'solve for power' marker; config systems defaulting unset fields to 0.

Related errors

• One and only one argument must be 0
• You cannot supply more or less than 2 values
• Capacitor at index {index} has a negative or zero value!
• You cannot supply more or less than 2 values
• Electron concentration cannot be negative in a semiconductor

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/eae16f9f70611435. Report an issue: GitHub.