donnemartin/interactive-coding-challenges · error · TypeError

Argument cannot be None

Error message

Argument cannot be None

What it means

Bits.insert_m_into_n raises TypeError('Argument cannot be None') when any of m, n, i, j is None. The routine builds masks and shifts m into a cleared window of n, so all four values must be present integers.

Source

Thrown at bit_manipulation/insert_m_into_n/insert_m_into_n_solution.ipynb:118

  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Bits(object):\n",
    "\n",
    "    def insert_m_into_n(self, m, n, i, j):\n",
    "        if None in (m, n, i, j):\n",
    "            raise TypeError('Argument cannot be None')\n",
    "        if i < 0 or j < 0:\n",
    "            raise ValueError('Index cannot be negative')\n",
    "        left_mask = -1 << (j + 1)\n",
    "        right_mask = (1 << i) - 1\n",
    "        n_mask = left_mask | right_mask\n",
    "        # Clear bits from j to i, inclusive\n",
    "        n_cleared = n & n_mask\n",
    "        # Shift m into place before inserting it into n\n",
    "        m_mask = m << i\n",
    "        return n_cleared | m_mask"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]

View on GitHub (pinned to 358f2cc604)

Solutions

1. Supply all four values explicitly, e.g. insert_m_into_n(0b10, 0b1000, 2, 4)
2. Validate the payload/spec object for missing fields before calling
3. Use dict.get with required-check or raise your own clearer error upstream

Example fix

# before
bits.insert_m_into_n(spec.get('m'), spec.get('n'), spec.get('i'), spec.get('j'))

# after
try:
    m, n, i, j = spec['m'], spec['n'], spec['i'], spec['j']
except KeyError as e:
    raise ValueError(f'missing field {e}')
bits.insert_m_into_n(m, n, i, j)

if None in (m, n, i, j):
    raise ValueError('m, n, i, j are all required')
bits.insert_m_into_n(m, n, i, j)

def all_present(*vals) -> bool:
    return all(v is not None for v in vals)

try:
    result = bits.insert_m_into_n(m, n, i, j)
except TypeError as e:
    if 'cannot be None' in str(e):
        raise ValueError('incomplete insert spec') from e
    raise

When it happens

Trigger: insert_m_into_n(None, 15, 2, 4), or calling with values unpacked from a tuple/dict that had fewer entries; optional parameters left as None.

Common situations: Parsing 'insert m into n between bits i and j' specs from config where a field is missing; parameter defaults introduced by refactoring.

Related errors

• Invalid argument: None
• num cannot be None
• num 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/727c9dd885d8a2ac. Report an issue: GitHub.