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   "metadata": {},
   "source": [
    "# PyTorch DataLoader State and Nested Iterations"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "37d57e04-facc-4543-9939-c724a57ce9c6",
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    {
     "data": {
      "text/plain": [
       "'2.1.0'"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import torch\n",
    "torch.__version__"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9fb9f618-f274-4f76-951f-40508cb85c1d",
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   "source": [
    "Iterating over a dataloader in a separate function will not affect its state in the main training loop. In PyTorch, a DataLoader is typically an iterable that can be iterated over multiple times independently. Each iteration over the DataLoader starts from the beginning and goes through the dataset in a fresh sequence (if shuffle is true, the sequence will be different each time).\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "1813f041-0366-4be3-890f-99c1a9c9d831",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "main loop: 1\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 2\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 3\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 4\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 5\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 6\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 7\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 8\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 9\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n",
      "main loop: 10\n",
      "nested loop: 1\n",
      "nested loop: 2\n",
      "nested loop: 3\n",
      "nested loop: 4\n",
      "nested loop: 5\n"
     ]
    }
   ],
   "source": [
    "from torch.utils.data import Dataset, DataLoader\n",
    "\n",
    "# Custom Dataset class\n",
    "class IntegerDataset(Dataset):\n",
    "    def __init__(self, start, end):\n",
    "        self.data = list(range(start, end + 1))\n",
    "\n",
    "    def __len__(self):\n",
    "        return len(self.data)\n",
    "\n",
    "    def __getitem__(self, idx):\n",
    "        return self.data[idx]\n",
    "\n",
    "# Create a Dataset for integers 1 to 10\n",
    "integer_dataset = IntegerDataset(1, 10)\n",
    "\n",
    "# Create a DataLoader\n",
    "integer_loader = DataLoader(integer_dataset, batch_size=1, shuffle=False)\n",
    "\n",
    "# A function to estimate the loss based on a subset of training examples\n",
    "def calc_loss(data_loader, iters):\n",
    "    for j in integer_loader:\n",
    "        print(\"nested loop:\", j.item())\n",
    "        if j >= iters: \n",
    "            break\n",
    "\n",
    "# Example: Iterate over the DataLoader\n",
    "for i in integer_loader:\n",
    "    print(\"main loop:\", i.item())\n",
    "    calc_loss(integer_loader, iters=5)"
   ]
  }
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