donnemartin/interactive-coding-challenges · error · TypeError

items cannot be None

Error message

items cannot be None

What it means

Raised by Anagram.group_anagrams when items is None. The method iterates items and builds an OrderedDict keyed by sorted character tuples, so a None list is rejected up front with a TypeError instead of failing inside the for loop.

Source

Thrown at sorting_searching/anagrams/anagrams_solution.ipynb:111

   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import OrderedDict\n",
    "\n",
    "\n",
    "class Anagram(object):\n",
    "\n",
    "    def group_anagrams(self, items):\n",
    "        if items is None:\n",
    "            raise TypeError('items cannot be None')\n",
    "        if not items:\n",
    "            return items\n",
    "        anagram_map = OrderedDict()\n",
    "        for item in items:\n",
    "            # Use a tuple, which is hashable and\n",
    "            # serves as the key in anagram_map\n",
    "            sorted_chars = tuple(sorted(item))\n",
    "            if sorted_chars in anagram_map:\n",
    "                anagram_map[sorted_chars].append(item)\n",
    "            else:\n",
    "                anagram_map[sorted_chars] = [item]\n",
    "        result = []\n",
    "        for value in anagram_map.values():\n",
    "            result.extend(value)\n",
    "        return result"
   ]
  },
  {

View on GitHub (pinned to 358f2cc604)

Solutions

1. Default to an empty list: items = items or []
2. Fix loaders to return [] instead of None on missing data
3. Check the source collection before calling

Example fix

// before
groups = anagram.group_anagrams(load_words(path))
// after
groups = anagram.group_anagrams(load_words(path) or [])

items = items or []
anagram.group_anagrams(items)

def is_str_list(x):
    return isinstance(x, list) and all(isinstance(i, str) for i in x)

try:
    anagram.group_anagrams(words)
except TypeError:
    groups = {}

When it happens

Trigger: Calling group_anagrams(None). An empty list is valid and returned as-is; only None raises.

Common situations: Word lists loaded from a file or API where the words field is missing; a list comprehension variable that stayed None; chaining after a function that returns None on failure.

Related errors

• num cannot be None
• max_num cannot be None
• val cannot be None
• n cannot be None
• a or b cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/0e6824e773008640. Report an issue: GitHub.