TheAlgorithms/Python · critical · ValueError

Parameter n must be greater than or equal to one.

Error message

Parameter n must be greater than or equal to one.

What it means

Documented ValueError from project_euler/problem_003/sol1.py:solution when n <= 0 after int conversion; the largest-prime-factor algorithm only accepts positive integers. CAVEAT: unreachable as shipped because the file's 'except TypeError, ValueError:' is Python 2 syntax and the module raises SyntaxError under Python 3 before this check runs.

Source

Thrown at project_euler/problem_003/sol1.py:86

    Traceback (most recent call last):
        ...
    ValueError: Parameter n must be greater than or equal to one.
    >>> solution([])
    Traceback (most recent call last):
        ...
    TypeError: Parameter n must be int or castable to int.
    >>> solution("asd")
    Traceback (most recent call last):
        ...
    TypeError: Parameter n must be int or castable to int.
    """

    try:
        n = int(n)
    except TypeError, ValueError:
        raise TypeError("Parameter n must be int or castable to int.")
    if n <= 0:
        raise ValueError("Parameter n must be greater than or equal to one.")
    max_number = 0
    if is_prime(n):
        return n
    while n % 2 == 0:
        n //= 2
    if is_prime(n):
        return n
    for i in range(3, int(math.sqrt(n)) + 1, 2):
        if n % i == 0:
            if is_prime(n // i):
                max_number = n // i
                break
            elif is_prime(i):
                max_number = i
    return max_number


if __name__ == "__main__":

View on GitHub (pinned to f5988cc097)

Solutions

1. Fix the except clause at project_euler/problem_003/sol1.py:84 to use parenthesized exceptions so the module imports.
2. Pass n >= 1 (1 is accepted; 2 returns 2 immediately).
3. Clamp user-derived input: n = max(n, 1) only if 1 is semantically acceptable, otherwise reject.
4. Catch ValueError for batch enumeration over possibly-invalid inputs.

Example fix

# before
solution(0)

# after
n = int(input_value)
if n <= 0:
    raise ValueError('n must be positive')
result = solution(n)

n = int(n)
if n < 1:
    raise ValueError('n must be a positive integer')
solution(n)

def is_valid_factorization_input(n) -> bool:
    return isinstance(n, int) and not isinstance(n, bool) and n >= 1

try:
    solution(n)
except ValueError as e:
    if 'greater than or equal to one' in str(e):
        ...

When it happens

Trigger: After the syntax fix: solution(0) or solution(-10). As written today: importing the module under Python 3 fails immediately with SyntaxError.

Common situations: Generic benchmark harnesses that call every solution with 0; negative values from subtracting user input without clamping; running the legacy file under a modern interpreter where the py2 syntax breaks first.

Related errors

• Parameter n must be greater than or equal to one.
• Parameter n must be greater than or equal to one.
• Parameter n must be greater than or equal to one.
• Parameter n must be int or castable to int.
• Parameter n must be int or castable to int.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/81c221dfa71b207b. Report an issue: GitHub.