TheAlgorithms/Python · error · ValueError

All resistance values must be positive

Error message

All resistance values must be positive

What it means

Raised by wheatstone_solver() in electronics/wheatstone_bridge.py when any of resistance_1, resistance_2, resistance_3 is <= 0. A Wheatstone bridge requires three known positive resistances to solve for the fourth (Rx = (R2/R1)*R3); zero or negative values make the ratio undefined or unphysical, hence the single guard covering all three parameters.

Source

Thrown at electronics/wheatstone_bridge.py:33

    ---------------

    Usage examples:
    >>> wheatstone_solver(resistance_1=2, resistance_2=4, resistance_3=5)
    10.0
    >>> wheatstone_solver(resistance_1=356, resistance_2=234, resistance_3=976)
    641.5280898876405
    >>> wheatstone_solver(resistance_1=2, resistance_2=-1, resistance_3=2)
    Traceback (most recent call last):
        ...
    ValueError: All resistance values must be positive
    >>> wheatstone_solver(resistance_1=0, resistance_2=0, resistance_3=2)
    Traceback (most recent call last):
        ...
    ValueError: All resistance values must be positive
    """

    if resistance_1 <= 0 or resistance_2 <= 0 or resistance_3 <= 0:
        raise ValueError("All resistance values must be positive")
    else:
        return float((resistance_2 / resistance_1) * resistance_3)


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Supply all three known arm resistances as positive numbers.
2. Check measurement plumbing when a channel reads 0 — that indicates an open input, not a valid resistance.
3. Validate all three at once upstream: `if min(r1, r2, r3) <= 0: raise` with a message naming the parameter.

Example fix

# before
wheatstone_solver(resistance_1=2, resistance_2=-1, resistance_3=2)  # ValueError

# after
rx = wheatstone_solver(resistance_1=2, resistance_2=1.0, resistance_3=2)

if min(resistance_1, resistance_2, resistance_3) <= 0:
    raise MeasurementError("All three known bridge arms must be positive")

def valid_bridge_arms(r1: float, r2: float, r3: float) -> bool:
    return min(r1, r2, r3) > 0

try:
    rx = wheatstone_solver(resistance_1=r1, resistance_2=r2, resistance_3=r3)
except ValueError as exc:
    rx = float("nan")
    flag_open_channel(exc)

When it happens

Trigger: wheatstone_solver(resistance_1=2, resistance_2=-1, resistance_3=2) or any parameter equal to 0; one arm left unset and defaulting to 0 in a form or CLI.

Common situations: Instrumentation setups where one arm's measured value is 0 because the bridge is unbalanced/unconnected; negative values from calibration offsets; forgetting that all three known arms must be supplied.

Related errors

• 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
• Hole concentration cannot be negative in a semiconductor
• Intrinsic concentration cannot be negative in a semiconducto

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/086bdc8028f0232f. Report an issue: GitHub.