TheAlgorithms/Python · error · ValueError

Capacitor at index {index} has a negative value!

Error message

Capacitor at index {index} has a negative value!

What it means

Raised by capacitor_parallel() (electronics/capacitor_equivalence.py:21) when a capacitor value in the list is negative. Capacitance is physically non-negative, and the function simply sums values (Ceq = C1+C2+...+Cn in parallel), so a negative entry is treated as bad data rather than mathematically continued. The message includes the offending index.

Source

Thrown at electronics/capacitor_equivalence.py:21

from __future__ import annotations


def capacitor_parallel(capacitors: list[float]) -> float:
    """
    Ceq = C1 + C2 + ... + Cn
    Calculate the equivalent resistance for any number of capacitors in parallel.
    >>> capacitor_parallel([5.71389, 12, 3])
    20.71389
    >>> capacitor_parallel([5.71389, 12, -3])
    Traceback (most recent call last):
        ...
    ValueError: Capacitor at index 2 has a negative value!
    """
    sum_c = 0.0
    for index, capacitor in enumerate(capacitors):
        if capacitor < 0:
            msg = f"Capacitor at index {index} has a negative value!"
            raise ValueError(msg)
        sum_c += capacitor
    return sum_c


def capacitor_series(capacitors: list[float]) -> float:
    """
    Ceq = 1/ (1/C1 + 1/C2 + ... + 1/Cn)
    >>> capacitor_series([5.71389, 12, 3])
    1.6901062252507735
    >>> capacitor_series([5.71389, 12, -3])
    Traceback (most recent call last):
        ...
    ValueError: Capacitor at index 2 has a negative or zero value!
    >>> capacitor_series([5.71389, 12, 0.000])
    Traceback (most recent call last):
        ...
    ValueError: Capacitor at index 2 has a negative or zero value!
    """

View on GitHub (pinned to f5988cc097)

Solutions

1. Remove or correct the negative entry: the error message's index tells you exactly which element to fix.
2. If -1 is your 'missing component' sentinel, filter it out before calling: [c for c in caps if c >= 0].
3. Validate component values at parse time with a physical-range check (0 to, say, 1 farad).

Example fix

# before
capacitor_parallel([5.71389, 12, -3])  # ValueError: index 2

# after
capacitor_parallel([5.71389, 12, 3])

def valid_capacitors(caps: list[float]) -> bool:
    return all(c >= 0 for c in caps)

try:
    capacitor_parallel(caps)
except ValueError as e:
    if 'negative' in str(e):
        idx = int(e.args[0].split('index ')[1].split(' ')[0])
        caps = [c for i, c in enumerate(caps) if i != idx]
    else:
        raise

When it happens

Trigger: Calling capacitor_parallel([5.71389, 12, -3]) exactly as in the doctest; any list where element i < 0 raises with that index. Zero values are accepted (they just contribute nothing). capacitor_series has its own analogous check.

Common situations: Netlist parsing where a missing component defaults to -1 as a sentinel; measurement data with sign-inverted readings; hand-entered parts lists with typos.

Related errors

• Donor concentration should be positive
• Acceptor concentration should be positive
• Intrinsic concentration should be positive
• Capacitor at index {index} has a negative or zero value!
• Expected a_coeffs to have {self.order + 1} elements for {sel

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/250f827fe57d2bbe. Report an issue: GitHub.