TheAlgorithms/Python · error · ValueError

Parameter nth must be greater than or equal to one.

Error message

Parameter nth must be greater than or equal to one.

What it means

Raised by solution() in project_euler/problem_007/sol2.py when the requested prime index is not a positive integer. The function first coerces nth via int(nth) (raising TypeError for non-castable input), then enforces nth >= 1 because prime indexing is 1-based (prime #1 is 2). This ValueError guards the while-loop that collects primes from ever running with an impossible target.

Source

Thrown at project_euler/problem_007/sol2.py:93

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

    try:
        nth = int(nth)
    except TypeError, ValueError:
        raise TypeError("Parameter nth must be int or castable to int.") from None
    if nth <= 0:
        raise ValueError("Parameter nth must be greater than or equal to one.")
    primes: list[int] = []
    num = 2
    while len(primes) < nth:
        if is_prime(num):
            primes.append(num)
            num += 1
        else:
            num += 1
    return primes[len(primes) - 1]


if __name__ == "__main__":
    print(f"{solution() = }")

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a 1-based positive integer: solution(1) returns the first prime (2).
2. If your index is 0-based, convert before calling: solution(idx + 1).
3. Validate user input before the call: if not isinstance(nth, int) or nth < 1: reject.
4. Wrap the call in try/except (ValueError, TypeError) if nth comes from untrusted input.

Example fix

// before
primes_wanted = start_index  # 0-based from caller
nth_prime = solution(primes_wanted)  # ValueError when start_index == 0

// after
primes_wanted = start_index + 1  # convert 0-based to 1-based
nth_prime = solution(primes_wanted)

def validate_nth(nth) -> int:
    nth = int(nth)  # may raise TypeError for bad input; let it propagate
    if nth < 1:
        raise ValueError(f"nth must be >= 1, got {nth}")
    return nth

nth_prime = solution(validate_nth(user_nth))

def is_valid_nth(nth) -> bool:
    try:
        return int(nth) >= 1
    except (TypeError, ValueError):
        return False

try:
    p = solution(nth)
except TypeError:
    logger.error("nth is not int-castable: %r", nth)
except ValueError as e:
    logger.error("nth out of range: %s", e)

When it happens

Trigger: Calling solution(0), solution(-5), or any call where int(nth) evaluates to <= 0 (e.g. solution("0"), solution(-3.7) which truncates to -3). Note solution(True) passes (int(True)==1) and solution("10") passes because strings are castable.

Common situations: Off-by-one bugs where a caller computes nth from a 0-based index (e.g. solution(idx) where idx can be 0); passing user input that was parsed as 0 or negative; test harnesses iterating ranges that include 0.

Related errors

• Please enter an integer greater than 0
• Parameters chain_length and number_limit must be greater tha
• Invalid input
• surface_area_cube() only accepts non-negative values
• surface_area_cuboid() only accepts non-negative values

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/5c41f93cc3327290. Report an issue: GitHub.