TheAlgorithms/Python · error · ValueError

multiplicative_persistence() does not accept negative values

Error message

multiplicative_persistence() does not accept negative values

What it means

multiplicative_persistence() in maths/persistence.py rejects negative inputs after confirming the value is an int: if num < 0 it raises ValueError('multiplicative_persistence() does not accept negative values'). Digit-product persistence is defined for non-negative integers, and str(-39) would inject a '-' character that breaks the int(i) digit parsing, so negatives are refused rather than mangled.

Source

Thrown at maths/persistence.py:22

    https://en.wikipedia.org/wiki/Persistence_of_a_number

    >>> multiplicative_persistence(217)
    2
    >>> multiplicative_persistence(-1)
    Traceback (most recent call last):
        ...
    ValueError: multiplicative_persistence() does not accept negative values
    >>> multiplicative_persistence("long number")
    Traceback (most recent call last):
        ...
    ValueError: multiplicative_persistence() only accepts integral values
    """

    if not isinstance(num, int):
        raise ValueError("multiplicative_persistence() only accepts integral values")
    if num < 0:
        raise ValueError("multiplicative_persistence() does not accept negative values")

    steps = 0
    num_string = str(num)

    while len(num_string) != 1:
        numbers = [int(i) for i in num_string]

        total = 1
        for i in range(len(numbers)):
            total *= numbers[i]

        num_string = str(total)

        steps += 1
    return steps


def additive_persistence(num: int) -> int:

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass the absolute value if sign is irrelevant: multiplicative_persistence(abs(num)).
2. Add an upstream range check (num >= 0) with your own error message if negatives indicate a bug in caller data.
3. Catch ValueError if negative input is expected occasionally and handle it explicitly.

Example fix

# before
multiplicative_persistence(value)  # ValueError when value == -39

# after
multiplicative_persistence(abs(value))

if num < 0:
    raise ValueError(f'persistence undefined for negative {num}')
multiplicative_persistence(num)

try:
    multiplicative_persistence(num)
except ValueError as exc:
    if 'negative' in str(exc):
        num = abs(num)  # only if sign is truly irrelevant
    else:
        raise

When it happens

Trigger: Calling multiplicative_persistence(-1) or any negative int such as multiplicative_persistence(-39). Only reached when the argument is an int; a negative float raises the integral-values error instead because the type check runs first.

Common situations: Feeding signed deltas or temperatures into the function; forgetting to abs() a value that can be negative by domain; off-by-one underflow producing -1 in a loop.

Related errors

• number must be an integer
• multiplicative_persistence() only accepts integral values
• additive_persistence() only accepts integral values
• additive_persistence() does not accept negative values
• is_prime() only accepts positive integers

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/a99c32854c7a769d. Report an issue: GitHub.