donnemartin/interactive-coding-challenges · error · TypeError

sentence cannot be None

Error message

sentence cannot be None

What it means

This TypeError is raised by the brute-force sentence screen fit solver when the sentence argument is None. It is a deliberate input-validation guard at the top of count_sentence_fit_brute_force, before any algorithm logic runs, because joining/iterating a None sentence would otherwise fail with a less clear AttributeError. It signals the caller passed no sentence data to the API.

Source

Thrown at online_judges/sentence_screen_fit/sentence_screen_fit_solution.ipynb:163

  },
  {
   "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",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass a valid list of sentence strings, e.g. ['hello', 'world']
2. Check the upstream variable that produces sentence and give it a default: sentence = sentence or []
3. Add a unit test asserting TypeError is raised for None to make the contract explicit

Example fix

// before
sol.count_sentence_fit_brute_force(None, 5, 10)
// after
sol.count_sentence_fit_brute_force(['hello', 'world'], 5, 10)

if sentence is None:
    raise ValueError('sentence input is required')
# or: sentence = sentence or []
count = sol.count_sentence_fit_brute_force(sentence, rows, cols)

def is_sentence_list(x):
    return isinstance(x, list) and all(isinstance(w, str) for w in x)

try:
    n = sol.count_sentence_fit_brute_force(sentence, rows, cols)
except TypeError as e:
    if 'sentence cannot be None' in str(e):
        n = 0  # nothing to fit
    else:
        raise

When it happens

Trigger: Calling Solution().count_sentence_fit_brute_force(None, rows, cols) with any rows/cols values; e.g. passing a variable that was initialized to None or a lookup that returned None from a dict of test sentences.

Common situations: Test harnesses iterating over optional inputs where the sentence key is missing; refactoring code so the sentence list is conditionally built and stays None on the empty path; JSON/YAML config where the sentences field was omitted.

Related errors

• rows and cols 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/fadb527a7606bc26. Report an issue: GitHub.