donnemartin/interactive-coding-challenges · error · TypeError

num cannot be None

Error message

num cannot be None

What it means

Bits.pairwise_swap raises TypeError('num cannot be None') when num is None. The method swaps even and odd bit pairs using fixed 0xAAAA/0x5555 masks and requires an integer operand.

Source

Thrown at bit_manipulation/pairwise_swap/pairwise_swap_solution.ipynb:118

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Bits(object):\n",
    "\n",
    "    def pairwise_swap(self, num):\n",
    "        if num is None:\n",
    "            raise TypeError('num cannot be None')\n",
    "        if num == 0 or num == 1:\n",
    "            return num\n",
    "        odd = (num & int('1010101010101010', base=2)) >> 1\n",
    "        even = (num & int('0101010101010101', base=2)) << 1\n",
    "        return odd | even"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass an int: pairwise_swap(0b1010)
2. Default safely: pairwise_swap(num or 0)
3. Fix the upstream source of the None value

Example fix

# before
swapped = bits.pairwise_swap(data.get('value'))

# after
value = data.get('value')
if value is None:
    raise ValueError("'value' required")
swapped = bits.pairwise_swap(value)

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

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

try:
    swapped = bits.pairwise_swap(num)
except TypeError:
    swapped = None

When it happens

Trigger: Bits().pairwise_swap(None), or passing an optional parameter, a None-returning lookup, or an uninitialized variable.

Common situations: Optional numeric fields flowing into the call; refactor that changed a required parameter to optional; test fixtures missing a value.

Related errors

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

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/aaaaf403cfd11834. Report an issue: GitHub.