donnemartin/interactive-coding-challenges · error · TypeError

greed_indices or cookie_sizes cannot be None

Error message

greed_indices or cookie_sizes cannot be None

What it means

Raised by Solution.find_content_children (LeetCode 'Assign Cookies') when greed_indices or cookie_sizes is None. Both lists are sorted and iterated, so None would crash with a confusing AttributeError; the guard makes the list contract explicit.

Source

Thrown at online_judges/assign_cookies/assign_cookies_solution.ipynb:128

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def find_content_children(self, greed_indices, cookie_sizes):\n",
    "        if greed_indices is None or cookie_sizes is None:\n",
    "            raise TypeError('greed_indices or cookie_sizes cannot be None')\n",
    "        if not greed_indices or not cookie_sizes:\n",
    "            return 0\n",
    "        greed_indices.sort()\n",
    "        cookie_sizes.sort()\n",
    "        greed_index = 0\n",
    "        num_children = 0\n",
    "        for size in cookie_sizes:\n",
    "            if greed_index >= len(greed_indices):\n",
    "                break\n",
    "            if size >= greed_indices[greed_index]:\n",
    "                num_children += 1\n",
    "                greed_index += 1\n",
    "        return num_children"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass two lists (possibly empty — empty lists correctly return 0)
2. Initialize variables to [] instead of None
3. Check for None and default to empty list before the call

Example fix

# before
solution.find_content_children(payload.get('g'), payload.get('s'))

# after
solution.find_content_children(payload.get('g') or [], payload.get('s') or [])

greed_indices = greed_indices or []
cookie_sizes = cookie_sizes or []
solution.find_content_children(greed_indices, cookie_sizes)

def is_list(x): return isinstance(x, list)

try:
    n = solution.find_content_children(g, s)
except TypeError:
    n = 0

When it happens

Trigger: Calling find_content_children(None, [1,2]) or with either list None — often from an optional argument, an empty initialization like greed = None, or a missing dict key.

Common situations: Test cases asserting the None guard; adapters receiving possibly-missing arrays from JSON payloads.

Related errors

• prices cannot be None
• num cannot be None
• max_num cannot be None
• val cannot be None
• n cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/f397d3bb41b281b3. Report an issue: GitHub.