donnemartin/interactive-coding-challenges · error · TypeError

array cannot be None

Error message

array cannot be None

What it means

Raised by Solution.max_prod_three_nlogn when array is None. The O(n log n) approach sorts the array in place and multiplies the last three elements, so a None input is rejected with TypeError before sorting would fail.

Source

Thrown at online_judges/prod_three/prod_three_solution.ipynb:155

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def max_prod_three_nlogn(self, array):\n",
    "        if array is None:\n",
    "            raise TypeError('array cannot be None')\n",
    "        if len(array) < 3:\n",
    "            raise ValueError('array must have 3 or more ints')\n",
    "        array.sort()\n",
    "        product = 1\n",
    "        for item in array[-3:]:\n",
    "            product *= item\n",
    "        return product\n",
    "\n",
    "    def max_prod_three(self, array):\n",
    "        if array is None:\n",
    "            raise TypeError('array cannot be None')\n",
    "        if len(array) < 3:\n",
    "            raise ValueError('array must have 3 or more ints')\n",
    "        curr_max_prod_three = array[0] * array[1] * array[2]\n",
    "        max_prod_two = array[0] * array[1]\n",
    "        min_prod_two = array[0] * array[1]\n",
    "        max_num = max(array[0], array[1])\n",
    "        min_num = min(array[0], array[1])\n",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Coalesce None to [] (then the length guard gives a clear ValueError) or filter the data source.
2. Check array is not None at the call site.
3. Pass sorted(array) or a copy if mutation of the original matters.

Example fix

# before
Solution().max_prod_three_nlogn(values)  # values may be None

# after
Solution().max_prod_three_nlogn(values or [])

if not array:
    array = []
best = Solution().max_prod_three_nlogn(array) if array else None

def is_int_list(x):
    return isinstance(x, list) and all(isinstance(v, int) for v in x)

try:
    Solution().max_prod_three_nlogn(array)
except TypeError as e:
    if 'cannot be None' in str(e):
        array = []
    else:
        raise

When it happens

Trigger: Calling max_prod_three_nlogn(None) or max_prod_three_nlogn() with an uninitialized variable.

Common situations: Optional numeric datasets (empty feed, missing column) flowing into the routine; also beware it mutates the caller's list via array.sort().

Related errors

• array cannot be None
• nums cannot be None
• array cannot be None
• ransom_note or magazine cannot be None
• sentence cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/9074546d21219f09. Report an issue: GitHub.