TheAlgorithms/Python · error · ValueError

number must be an integer

Error message

number must be an integer

What it means

Raised by perfect(number) in maths/special_numbers/perfect_number.py when the argument is not an int. Unusually, this is a ValueError rather than a TypeError — the library uses ValueError for both type and range problems, so catching TypeError alone will miss it. Inputs <= 0 do not raise; they return False.

Source

Thrown at maths/special_numbers/perfect_number.py:61

    >>> perfect(496)
    True
    >>> perfect(8128)
    True
    >>> perfect(0)
    False
    >>> perfect(-1)
    False
    >>> perfect(12.34)
    Traceback (most recent call last):
      ...
    ValueError: number must be an integer
    >>> perfect("Hello")
    Traceback (most recent call last):
      ...
    ValueError: number must be an integer
    """
    if not isinstance(number, int):
        raise ValueError("number must be an integer")
    if number <= 0:
        return False
    return sum(i for i in range(1, number // 2 + 1) if number % i == 0) == number


if __name__ == "__main__":
    from doctest import testmod

    testmod()
    print("Program to check whether a number is a Perfect number or not...")
    try:
        number = int(input("Enter a positive integer: ").strip())
    except ValueError:
        msg = "number must be an integer"
        print(msg)
        raise ValueError(msg)

    print(f"{number} is {'' if perfect(number) else 'not '}a Perfect Number.")

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass only builtin ints: convert with int() after confirming the value is integral
2. Catch ValueError (not TypeError) around this function if you must handle bad input
3. Normalize inputs at your boundary: reject non-integers before calling

Example fix

// before
try:
    perfect('12')  # ValueError, not TypeError
except TypeError:
    ...  # never reached

// after
try:
    perfect(int('12'))
except ValueError:
    ...

if not isinstance(n, int) or isinstance(n, bool):
    raise ValueError('perfect() requires a builtin int')
print(perfect(n))

def is_valid_perfect_input(v) -> TypeGuard[int]:
    return isinstance(v, int) and not isinstance(v, bool)

try:
    perfect(n)
except ValueError as e:  # type errors ALSO come out as ValueError here
    if 'integer' in str(e):
        n = int(n)
    else:
        raise

When it happens

Trigger: Calling perfect(12.34) or perfect('Hello'). bool passes the isinstance(number, int) check (True is treated as 1, False as 0 -> False).

Common situations: Calling code that assumes the conventional TypeError for bad types and catches the wrong exception class; float inputs from measurements or JSON.

Related errors

• surface_area_cube() only accepts non-negative values
• surface_area_cuboid() only accepts non-negative values
• surface_area_sphere() only accepts non-negative values
• surface_area_hemisphere() only accepts non-negative values
• surface_area_cone() only accepts non-negative values

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/b96e38e3c4c6ea1b. Report an issue: GitHub.