donnemartin/interactive-coding-challenges · error · TypeError

num cannot be None

Error message

num cannot be None

What it means

Raised by Solution.fizz_buzz when num is None. The method iterates range(1, num+1), so None would fail comparison; the guard rejects it up front with a clear TypeError. num must be a positive integer.

Source

Thrown at arrays_strings/fizz_buzz/fizz_buzz_solution.ipynb:115

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def fizz_buzz(self, num):\n",
    "        if num is None:\n",
    "            raise TypeError('num cannot be None')\n",
    "        if num < 1:\n",
    "            raise ValueError('num cannot be less than one')\n",
    "        results = []\n",
    "        for i in range(1, num + 1):\n",
    "            if i % 3 == 0 and i % 5 == 0:\n",
    "                results.append('FizzBuzz')\n",
    "            elif i % 3 == 0:\n",
    "                results.append('Fizz')\n",
    "            elif i % 5 == 0:\n",
    "                results.append('Buzz')\n",
    "            else:\n",
    "                results.append(str(i))\n",
    "        return results"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},

View on GitHub (pinned to 358f2cc604)

Solutions

1. Validate and convert input to int before calling (e.g. int(request.args['n']))
2. Default None to a sensible value like 0 or 1 depending on desired behavior
3. Use argument parsing that enforces a required integer

Example fix

# before
Solution().fizz_buzz(params.get('n'))

# after
n = int(params['n'])
Solution().fizz_buzz(n)

if num is not None:
    Solution().fizz_buzz(num)

def is_positive_int(num) -> bool:
    return isinstance(num, int) and num >= 1

try:
    Solution().fizz_buzz(num)
except TypeError:
    num = 1  # or return an error to the caller

When it happens

Trigger: Calling fizz_buzz(None); passing an unset counter or a value parsed from unvalidated input.

Common situations: CLI/script arguments not converted to int; API handlers forwarding optional query params directly.

Related errors

• data cannot be None
• neighbor or weight cannot be None
• neighbor cannot be None
• key cannot be None
• key cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/1adb15563bca35d7. Report an issue: GitHub.