TheAlgorithms/Python · info · ValueError

Exactly one argument must be 0

Error message

Exactly one argument must be 0

What it means

The final else branch of ind_reactance() raises 'Exactly one argument must be 0'. It is unreachable defensive code: the leading guard `(inductance, frequency, reactance).count(0) != 1` already raises for any input without exactly one zero, so after the three negativity checks one of inductance==0 / frequency==0 / reactance==0 must hold. It exists only as a safety net, and its message text differs from the primary guard's.

Source

Thrown at electronics/ind_reactance.py:63

    """

    if (inductance, frequency, reactance).count(0) != 1:
        raise ValueError("One and only one argument must be 0")
    if inductance < 0:
        raise ValueError("Inductance cannot be negative")
    if frequency < 0:
        raise ValueError("Frequency cannot be negative")
    if reactance < 0:
        raise ValueError("Inductive reactance cannot be negative")
    if inductance == 0:
        return {"inductance": reactance / (2 * pi * frequency)}
    elif frequency == 0:
        return {"frequency": reactance / (2 * pi * inductance)}
    elif reactance == 0:
        return {"reactance": 2 * pi * frequency * inductance}
    else:
        raise ValueError("Exactly one argument must be 0")


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. No caller action required — the primary ValueError('One and only one argument must be 0') is the one you will observe.
2. Maintainers: remove the unreachable else or unify its message with the primary guard.
3. Test suites: exclude this branch from coverage targets rather than contorting inputs to reach it.

Example fix

# before
    elif reactance == 0:
        return {"reactance": 2 * pi * frequency * inductance}
    else:
        raise ValueError("Exactly one argument must be 0")

# after
    else:  # reactance == 0, the only remaining case
        return {"reactance": 2 * pi * frequency * inductance}

# Guard the reachable primary error instead:
assert (inductance, frequency, reactance).count(0) == 1

When it happens

Trigger: Cannot be triggered through the public API for any real inputs; only relevant if the initial count guard is removed/modified or in exhaustive branch-coverage tooling.

Common situations: Seen during code review, refactoring, or coverage/mutation testing; a fork that relaxes the first guard would surface the inconsistent second message.

Related errors

• Exactly one argument must be 0
• Exactly one argument must be 0
• Exactly one argument must be 0
• One and only one argument must be 0
• Inductance cannot be negative

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/1823da317a084329. Report an issue: GitHub.