donnemartin/interactive-coding-challenges · error · TypeError

number cannot be None

Error message

number cannot be None

What it means

The Bit class constructor raises TypeError('number cannot be None') when instantiated without a valid integer. This is defensive input validation ensuring self.number always holds an integer before bit operations run.

Source

Thrown at bit_manipulation/bit/bit_solution.ipynb:204

    "    def validate_index_wrapper(self, *args, **kwargs):\n",
    "        for arg in args:\n",
    "            if arg < 0:\n",
    "                raise IndexError('Invalid index')\n",
    "        return func(self, *args, **kwargs)\n",
    "    return validate_index_wrapper"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Bit(object):\n",
    "\n",
    "    def __init__(self, number):\n",
    "        if number is None:\n",
    "            raise TypeError('number cannot be None')\n",
    "        self.number = number\n",
    "\n",
    "    @validate_index\n",
    "    def get_bit(self, index):\n",
    "        mask = 1 << index\n",
    "        return self.number & mask != 0\n",
    "\n",
    "    @validate_index\n",
    "    def set_bit(self, index):\n",
    "        mask = 1 << index\n",
    "        self.number |= mask\n",
    "        return self.number\n",
    "\n",
    "    @validate_index\n",
    "    def clear_bit(self, index):\n",
    "        mask = ~(1 << index)\n",
    "        self.number &= mask\n",
    "        return self.number\n",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass an actual int, e.g. Bit(12)
2. Default the value: Bit(number or 0)
3. Validate upstream data source so number is never None

Example fix

# before
b = Bit(data.get('flags'))

# after
flags = data.get('flags')
if flags is None:
    raise ValueError("missing 'flags' in data")
b = Bit(flags)

if number is None:
    raise ValueError('number is required')
bit = Bit(number)

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

try:
    bit = Bit(number)
except TypeError as e:
    if 'cannot be None' in str(e):
        number = 0
        bit = Bit(number)
    else:
        raise

When it happens

Trigger: Bit(None), Bit(number) where number came from an uninitialized variable or a dict.get() that returned None, or forgetting the constructor argument entirely (which raises TypeError for the missing param instead).

Common situations: Loading values from JSON/config where a key is missing (dict.get returns None), passing an optional parameter straight through, or refactoring that changed the constructor signature.

Related errors

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

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/667e48e2b0d968aa. Report an issue: GitHub.