donnemartin/interactive-coding-challenges · error · TypeError

nums or target cannot be None

Error message

nums or target cannot be None

What it means

Raised by Solution.two_sum when nums or target is None. The method caches complements while scanning nums, so both must be valid; None is rejected with TypeError before any logic runs. Note the separate ValueError for empty nums lists.

Source

Thrown at arrays_strings/two_sum/two_sum_solution.ipynb:166

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def two_sum(self, nums, target):\n",
    "        if nums is None or target is None:\n",
    "            raise TypeError('nums or target cannot be None')\n",
    "        if not nums:\n",
    "            raise ValueError('nums cannot be empty')\n",
    "        cache = {}\n",
    "        for index, num in enumerate(nums):\n",
    "            cache_target = target - num\n",
    "            if num in cache:\n",
    "                return [cache[num], index]\n",
    "            else:\n",
    "                cache[cache_target] = index\n",
    "        return None"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]

View on GitHub (pinned to 358f2cc604)

Solutions

1. Validate both parameters at the call boundary before invoking two_sum
2. Return an explicit error/empty result to the caller when either is missing
3. Fix the producer so target is always computed (e.g. not data.get('target'))

Example fix

# before
Solution().two_sum(nums, params.get('target'))

# after
target = params.get('target')
if nums is not None and target is not None:
    result = Solution().two_sum(nums, target)

if nums is not None and target is not None:
    Solution().two_sum(nums, target)

def valid_two_sum_input(nums, target) -> bool:
    return nums is not None and target is not None

try:
    Solution().two_sum(nums, target)
except TypeError:
    return []  # or surface a validation error

When it happens

Trigger: Calling two_sum(None, 9) or two_sum([2,7], None); forwarding unset request parameters.

Common situations: API handlers passing optional nums/target params unvalidated; data pipelines where the array or target comes from an optional field.

Related errors

• data cannot be None
• str1 or str2 cannot be None
• neighbor or weight cannot be None
• neighbor cannot be None
• key cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/b0239e0d1315f8a7. Report an issue: GitHub.