donnemartin/interactive-coding-challenges · error · TypeError

a or b cannot be None

Error message

a or b cannot be None

What it means

Bits.bits_to_flip raises TypeError when either integer a or b is None. The method counts differing bits (Hamming distance) via a ^ b, which would fail on None, so inputs are validated up front.

Source

Thrown at bit_manipulation/bits_to_flip/bits_to_flip_solution.ipynb:101

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Bits(object):\n",
    "\n",
    "    def bits_to_flip(self, a, b):\n",
    "        if a is None or b is None:\n",
    "            raise TypeError('a or b cannot be None')\n",
    "        count = 0\n",
    "        c = a ^ b\n",
    "        while c:\n",
    "            count += c & 1\n",
    "            c >>= 1\n",
    "        return count"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,

View on GitHub (pinned to 358f2cc604)

Solutions

1. Ensure both arguments are ints before calling; supply defaults (a or 0)
2. Add an upstream null check on the data producing a and b
3. Catch TypeError if None is a legitimate sentinel you handle elsewhere

Example fix

# before
flips = bits.bits_to_flip(old_flags, new_flags)

# after
if old_flags is None or new_flags is None:
    raise ValueError('both flag values are required')
flips = bits.bits_to_flip(old_flags, new_flags)

if a is None or b is None:
    raise ValueError('both a and b are required')
Bits().bits_to_flip(a, b)

def both_ints(*vals) -> bool:
    return all(isinstance(v, int) and not isinstance(v, bool) for v in vals)

try:
    count = bits.bits_to_flip(a, b)
except TypeError:
    count = None  # one side missing; skip comparison

When it happens

Trigger: Bits().bits_to_flip(None, 5), bits_to_flip(a, None), or calling with values obtained from optional fields, optional function params, or dict lookups that returned None.

Common situations: Comparing two config versions or flags where one side is missing a key; optional numeric parameters flowing straight into the comparison.

Related errors

• number 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/5c2710502c962b4b. Report an issue: GitHub.