donnemartin/interactive-coding-challenges · error · TypeError

prices or k cannot be None

Error message

prices or k cannot be None

What it means

Raised by StockTrader.find_max_profit when prices or k is None. The method allocates a DP table with num_rows = k + 1 and num_cols = len(prices) on the next lines, so None inputs are rejected up front with a clear TypeError before table construction.

Source

Thrown at recursion_dynamic/max_profit_k/max_profit_solution.ipynb:168

    "        return str(self.type) + ' day: ' + \\\n",
    "            str(self.day) + ' price: ' + \\\n",
    "            str(self.price)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "import sys\n",
    "\n",
    "\n",
    "class StockTrader(object):\n",
    "\n",
    "    def find_max_profit(self, prices, k):\n",
    "        if prices is None or k is None:\n",
    "            raise TypeError('prices or k cannot be None')\n",
    "        if not prices or k <= 0:\n",
    "            return []\n",
    "        num_rows = k + 1  # 0th transaction for dp table\n",
    "        num_cols = len(prices)\n",
    "        T = [[None] * num_cols for _ in range(num_rows)]\n",
    "        for i in range(num_rows):\n",
    "            for j in range(num_cols):\n",
    "                if i == 0 or j == 0:\n",
    "                    T[i][j] = 0\n",
    "                    continue\n",
    "                max_profit = -sys.maxsize\n",
    "                for m in range(j):\n",
    "                    profit = prices[j] - prices[m] + T[i - 1][m]\n",
    "                    if profit > max_profit:\n",
    "                        max_profit = profit\n",
    "                T[i][j] = max(T[i][j - 1], max_profit)\n",
    "        return self._find_max_profit_transactions(T, prices)\n",
    "\n",

View on GitHub (pinned to 358f2cc604)

Solutions

1. Pass a numeric price list and an int k, defaulting missing values (prices = prices or [], k = k or 0)
2. Check the fetch result before computing: if prices is None: handle error
3. Validate parsed market data shape at ingestion

Example fix

// before
trades = trader.find_max_profit(fetch_prices(sym), k=None)
// after
prices = fetch_prices(sym)
if prices is None:
    prices = []
trades = trader.find_max_profit(prices, k=2)

if prices is None or k is None:
    return []
trader.find_max_profit(prices, k)

def valid_trader_args(prices, k):
    return isinstance(prices, list) and isinstance(k, int) and k > 0

try:
    trader.find_max_profit(prices, k)
except TypeError:
    trades = []

When it happens

Trigger: Calling find_max_profit(None, 2) or find_max_profit(prices, None). Empty prices or k <= 0 returns [] without raising — only None triggers the error.

Common situations: Price series fetched from an API that returned an error body; k left as None from optional config; reusing a data loader that signals failure with None.

Related errors

• coins or total cannot be None
• input_items or total_weight cannot be None
• items or total_weight cannot be None
• str input cannot be None
• seq cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/8af19dd10a01e50a. Report an issue: GitHub.