donnemartin/interactive-coding-challenges · error · TypeError

val cannot be None

Error message

val cannot be None

What it means

Raised by MathOps.insert in the online_judges variant when val is None (note this variant also has a typo'd attribute mode_ocurrences). The structure maintains running mean/min/max/mode counts that assume numeric input, so None is rejected before any accumulator is touched.

Solutions

1. Filter or replace None values before inserting
2. Fix parsing to skip missing entries
3. Guard at the call site: if val is not None: ops.insert(val)

Example fix

# before
for val in stream:
    ops.insert(val)  # stream may yield None

# after
for val in stream:
    if val is not None:
        ops.insert(val)

for v in values:
    if v is None: continue
    ops.insert(v)

def is_number(v): return isinstance(v, (int, float))

try:
    ops.insert(v)
except TypeError as e:
    logger.warning('skipping invalid value: %s', e)

When it happens

Trigger: Calling insert(None) — inserting values from a stream/dataset with missing entries (JSON null, CSV blank, failed parse).

Common situations: Streaming ingest of dirty data; batch tests; wrappers forwarding optional values unchanged.

Related errors

• val cannot be None
• a or b cannot be None
• a or b cannot be None
• data cannot be None
• file_system cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/a86f6b5bd1df9d64. Report an issue: GitHub.

Appendix: source

Thrown at online_judges/math_ops/math_ops_solution.ipynb:110

    "\n",
    "\n",
    "class Solution(object):\n",
    "\n",
    "    def __init__(self, upper_limit=100):\n",
    "        self.max = None\n",
    "        self.min = None\n",
    "        # Mean\n",
    "        self.num_items = 0\n",
    "        self.running_sum = 0\n",
    "        self.mean = None\n",
    "        # Mode\n",
    "        self.array = [0] * (upper_limit+1)\n",
    "        self.mode_ocurrences = 0\n",
    "        self.mode = None\n",
    "\n",
    "    def insert(self, val):\n",
    "        if val is None:\n",
    "            raise TypeError('val cannot be None')\n",
    "        if self.max is None or val > self.max:\n",
    "            self.max = val\n",
    "        if self.min is None or val < self.min:\n",
    "            self.min = val\n",
    "        # Calculate the mean\n",
    "        self.num_items += 1\n",
    "        self.running_sum += val\n",
    "        self.mean = self.running_sum / self.num_items\n",
    "        # Calculate the mode\n",
    "        self.array[val] += 1\n",
    "        if self.array[val] > self.mode_ocurrences:\n",
    "            self.mode_ocurrences = self.array[val]\n",
    "            self.mode = val"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},

View on GitHub (pinned to 358f2cc604)