donnemartin/interactive-coding-challenges · error · TypeError

num cannot be None

Error message

num cannot be None

What it means

Bits.get_next_largest raises TypeError('num cannot be None') when num is None. It computes the next larger integer with the same number of 1 bits, and the bit-counting loops require an actual integer.

Source

Thrown at bit_manipulation/get_next/get_next_solution.ipynb:118

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Bits(object):\n",
    "\n",
    "    def get_next_largest(self, num):\n",
    "        if num is None:\n",
    "            raise TypeError('num cannot be None')\n",
    "        if num <= 0:\n",
    "            raise ValueError('num cannot be 0 or negative')\n",
    "        num_ones = 0\n",
    "        num_zeroes = 0\n",
    "        num_copy = num\n",
    "        # We'll look for index, which is the right-most non-trailing zero\n",
    "        # Count number of zeroes to the right of index\n",
    "        while num_copy != 0 and num_copy & 1 == 0:\n",
    "            num_zeroes += 1\n",
    "            num_copy >>= 1\n",
    "        # Count number of ones to the right of index\n",
    "        while num_copy != 0 and num_copy & 1 == 1:\n",
    "            num_ones += 1\n",
    "            num_copy >>= 1\n",
    "        # Determine index and set the bit\n",
    "        index = num_zeroes + num_ones\n",
    "        num |= 1 << index\n",
    "        # Clear all bits to the right of index\n",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Supply a positive int, e.g. get_next_largest(6)
2. Use a safe default: get_next_largest(num if num is not None else 1)
3. Guard the data source so num is always set

Example fix

# before
nxt = bits.get_next_largest(data.get('value'))

# after
val = data.get('value')
if val is None:
    raise ValueError("'value' missing")
nxt = bits.get_next_largest(val)

if num is None:
    raise ValueError('num is required')
bits.get_next_largest(num)

def is_positive_int(v) -> bool:
    return isinstance(v, int) and not isinstance(v, bool) and v > 0

try:
    nxt = bits.get_next_largest(num)
except TypeError:
    nxt = None

When it happens

Trigger: Bits().get_next_largest(None), or passing a value from dict.get(), an optional parameter default of None, or an uninitialized variable.

Common situations: Feeding optional config numbers directly into the API; a refactor that made the parameter optional without adding a default at call sites.

Related errors

• Invalid argument: None
• num cannot be None
• Argument cannot be None
• num cannot be None
• number cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/ecd64aca14323244. Report an issue: GitHub.