donnemartin/interactive-coding-challenges · error · TypeError

rows and cols cannot be None

Error message

rows and cols cannot be None

What it means

Raised when rows or cols (or both) are None in the brute-force sentence screen fit solver. The method validates rows and cols immediately after the sentence check and rejects None because comparing None with 0 later would raise TypeError anyway. The guard makes the failure explicit and attributable at the API boundary.

Source

Thrown at online_judges/sentence_screen_fit/sentence_screen_fit_solution.ipynb:165

   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "\n",
    "    def count_sentence_fit_brute_force(self, sentence, rows, cols):\n",
    "        if sentence is None:\n",
    "            raise TypeError('sentence cannot be None')\n",
    "        if rows is None or cols is None:\n",
    "            raise TypeError('rows and cols cannot be None')\n",
    "        if rows < 0 or cols < 0:\n",
    "            raise ValueError('rows and cols cannot be negative')\n",
    "        if cols == 0 or not sentence:\n",
    "            return 0\n",
    "        curr_row = 0\n",
    "        curr_col = 0\n",
    "        count = 0\n",
    "        while curr_row < cols:\n",
    "            for word in sentence:\n",
    "                # If the current word doesn't fit on the current line,\n",
    "                # move to the next line\n",
    "                if len(word) > cols - curr_col:\n",
    "                    curr_col = 0\n",
    "                    curr_row += 1\n",
    "                # If we are beyond the number of rows, return\n",
    "                if curr_row >= rows:\n",
    "                    return count\n",
    "                # If the current word fits on the current line,\n",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass concrete non-negative integers for rows and cols
2. If dimensions are optional upstream, default them explicitly (rows = rows if rows is not None else 0) before calling
3. Validate parsed config values before invoking the solver

Example fix

// before
sol.count_sentence_fit_brute_force(['hi'], None, None)
// after
sol.count_sentence_fit_brute_force(['hi'], rows=3, cols=8)

assert isinstance(rows, int) and isinstance(cols, int), 'rows and cols must be ints'
sol.count_sentence_fit_brute_force(sentence, rows, cols)

def valid_dims(rows, cols):
    return isinstance(rows, int) and isinstance(cols, int) and not isinstance(rows, bool) and not isinstance(cols, bool)

try:
    sol.count_sentence_fit_brute_force(sentence, rows, cols)
except TypeError as e:
    if 'rows and cols cannot be None' in str(e):
        rows, cols = 0, 0  # sensible no-screen default
    else:
        raise

When it happens

Trigger: Calling count_sentence_fit_brute_force(sentence, None, 10) or (sentence, 5, None), typically when dimensions come from optional config or a function that returns None on failure to parse screen size.

Common situations: Reading screen dimensions from argparse/int() where the value is missing; a caller swapping argument order so None lands in rows/cols; defaults of None used as 'not specified' sentinels reaching the algorithm.

Related errors

• sentence cannot be None
• prices must have at least two values
• array cannot be None
• array must have 3 or more ints
• rows and cols cannot be negative

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/8b5919182c7cf5c7. Report an issue: GitHub.