donnemartin/interactive-coding-challenges · error · TypeError

n cannot be None

Error message

n cannot be None

What it means

Raised by Solution.is_power_of_two when n is None. The bit trick n & (n - 1) requires an integer; None would fail with a less clear TypeError, so the method enforces its contract explicitly.

Source

Thrown at math_probability/power_two/power_two_solution.ipynb:108

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def is_power_of_two(self, n):\n",
    "        if n is None:\n",
    "            raise TypeError('n cannot be None')\n",
    "        if n <= 0:\n",
    "            return False\n",
    "        return (n & (n - 1)) == 0"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass an integer: is_power_of_two(64)
2. Check for None at the call site and default or skip
3. Fix the upstream producer returning None

Example fix

# before
solution.is_power_of_two(nums.get(i))  # None when i missing

# after
n = nums.get(i)
if n is not None:
    solution.is_power_of_two(n)

if n is None: return False
solution.is_power_of_two(n)

def is_int(n): return isinstance(n, int)

try:
    solution.is_power_of_two(n)
except TypeError:
    result = False

When it happens

Trigger: Calling is_power_of_two(None) — an unset variable, a None default, or a value from a lookup that missed (dict.get, next(iter, None)).

Common situations: Interview test harnesses hitting edge cases; passing optional config flags through without defaults.

Related errors

• a or b cannot be None
• a or b cannot be None
• Invalid argument: None
• num cannot be None
• num cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/e7d85cdcc08a8b89. Report an issue: GitHub.