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    "# Python performance optimization"
   ]
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    "## Membership testing is faster in dict than in list. \n",
    "\n",
    "Python dictionaries use hash tables, this means that a lookup operation (e.g., if x in y) is O(1). A lookup operation in a list means that the entire list needs to be iterated, resulting in O(n) for a list of length n. http://www.clips.ua.ac.be/tutorials/python-performance-optimization"
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   "source": [
    "import timeit\n",
    "def test_ifin(d):\n",
    "    if 5000 in d:\n",
    "        a = 1\n",
    "    else:\n",
    "        a = 2\n",
    "\n",
    "d1 = dict.fromkeys(range(10000), True)\n",
    "d2 = range(10000)"
   ]
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     "text": [
      "0.000880002975464\n",
      "0.0672550201416\n"
     ]
    }
   ],
   "source": [
    "print (timeit.timeit(lambda: test_ifin(d1), number=1000))\n",
    "print (timeit.timeit(lambda: test_ifin(d2), number=1000))"
   ]
  },
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