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   "source": [
    "# CacheStack\n",
    "\n",
    "A `CacheStack` allows combining multiple caches into a single prioritized hierarchy.\n",
    "It is a common pattern to combine a fast, local cache (like an in-memory cache) with a larger, slower, and potentially remote cache (like a database or file system).\n",
    "\n",
    "## Automatic Hit Transfer\n",
    "\n",
    "Whenever a hit is found in a higher-level cache, it is automatically transferred to the base cache (index 0). This ensures that frequently accessed data migrates to the fastest cache in your stack."
   ]
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     "shell.execute_reply": "2026-03-22T19:56:32.047930Z"
    }
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   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "No config file found. Using default memory cache.\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "() ()\n",
      "Computing 42...\n",
      "Remote cache contains 42: True\n",
      "Local cache contains 42:  False\n"
     ]
    }
   ],
   "source": [
    "import tempfile\n",
    "import os\n",
    "from fleche import fleche, cache\n",
    "from fleche.caches import Cache, CacheStack\n",
    "from fleche.storage import Memory, PickleFile\n",
    "from fleche.storage.sql import Sql\n",
    "\n",
    "# 1. Setup a 'remote' persistent cache\n",
    "tmp_dir = tempfile.TemporaryDirectory()\n",
    "# Use PickleFile for values and Sql for calls to simulate a robust remote storage\n",
    "remote_storage_values = PickleFile.with_cloudpickle(tmp_dir.name)\n",
    "remote_storage_calls = Sql(f\"sqlite:///{os.path.join(tmp_dir.name, 'cache.db')}\")\n",
    "remote_cache = Cache(remote_storage_values, remote_storage_calls)\n",
    "\n",
    "# 2. Setup a 'local' fast memory cache\n",
    "local_cache = Cache(Memory({}), Memory({}))\n",
    "\n",
    "@fleche\n",
    "def expensive_computation(x):\n",
    "    print(f\"Computing {x}...\")\n",
    "    return x * 10\n",
    "\n",
    "# Pre-populate the remote cache\n",
    "with cache(remote_cache):\n",
    "    expensive_computation(42)\n",
    "\n",
    "print(\"Remote cache contains 42:\", remote_cache.contains(expensive_computation.digest(42)))\n",
    "print(\"Local cache contains 42: \", local_cache.contains(expensive_computation.digest(42)))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Creating the stack\n",
    "We prioritize `local_cache` over `remote_cache` by putting it at the front of the stack."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "execution": {
     "iopub.execute_input": "2026-03-22T19:56:32.050884Z",
     "iopub.status.busy": "2026-03-22T19:56:32.050559Z",
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     "shell.execute_reply": "2026-03-22T19:56:32.058544Z"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Calling expensive_computation(42) via stack...\n",
      "Result: 420\n",
      "Local cache now contains 42: True\n"
     ]
    }
   ],
   "source": [
    "stack = CacheStack((local_cache, remote_cache))\n",
    "\n",
    "with cache(stack):\n",
    "    # Loading 42 will hit remote_cache and automatically transfer it to local_cache\n",
    "    print(\"Calling expensive_computation(42) via stack...\")\n",
    "    result = expensive_computation(42)\n",
    "    print(f\"Result: {result}\")\n",
    "\n",
    "print(\"Local cache now contains 42:\", local_cache.contains(expensive_computation.digest(42)))\n",
    "\n",
    "# Cleanup\n",
    "tmp_dir.cleanup()"
   ]
  }
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