array.ipynb

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   "source": [
    "# Array"
   ]
  },
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   "cell_type": "markdown",
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   "source": [
    "##  Low level array"
   ]
  },
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   "cell_type": "markdown",
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   "source": [
    "###  Referential array"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "In python, when you copy an array to new array, both array elements refer to same object. But for immutable object, when you change one element of first array, the element in second array not change. "
   ]
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   "outputs": [
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     "name": "stdout",
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     "text": [
      "[1, 2, 10]\n",
      "[1, 2, 3]\n"
     ]
    }
   ],
   "source": [
    "array1 = [1 , 2 , 3 ]\n",
    "array2 = list(array1)\n",
    "\n",
    "array1[2] = 10\n",
    "\n",
    "print(array1)\n",
    "print(array2)"
   ]
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   },
   "source": [
    "### Compact array"
   ]
  },
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   "cell_type": "markdown",
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   "source": [
    "Because some time referential array is not good for storaga. Python creates new class array to store data. It is called compact array.\n"
   ]
  },
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   "execution_count": 7,
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     "text": [
      "92\n",
      "120\n"
     ]
    }
   ],
   "source": [
    "import sys\n",
    "\n",
    "primes = array.array('i', [2 , 3, 5, 7 ,9, 11, 13])\n",
    "print(sys.getsizeof(primes))\n",
    "\n",
    "\n",
    "list_primes = [2 , 3, 5, 7 ,9, 11, 13]\n",
    "print(sys.getsizeof(list_primes))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Dynamic array and amotization"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "System create array and reserve some space for futher element\n"
   ]
  },
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   "cell_type": "code",
   "execution_count": 11,
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    {
     "name": "stdout",
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     "text": [
      "Length   0; Size in bytes:   64\n",
      "Length   1; Size in bytes:   96\n",
      "Length   2; Size in bytes:   96\n",
      "Length   3; Size in bytes:   96\n",
      "Length   4; Size in bytes:   96\n"
     ]
    }
   ],
   "source": [
    "import sys\n",
    "data = []\n",
    "for k in range(5):\n",
    "    a = len(data)\n",
    "    b = sys.getsizeof(data)\n",
    "    print('Length {0:3d}; Size in bytes: {1:4d}'.format(a,b))\n",
    "    data.append(None)\n"
   ]
  },
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   "execution_count": 1,
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   "source": [
    "import ctypes\n",
    "\n",
    "class DynamicArray:\n",
    "    \"\"\"A dynamic array class akin to a simplified Python list\"\"\"\n",
    "    def __init__(self):\n",
    "        self._n = 0\n",
    "        self._capacity = 1\n",
    "        self._A = self._make_array(self._capacity)\n",
    "        \n",
    "    def __len__(self):\n",
    "        return self._n\n",
    "    \n",
    "    def __getitem__(self, k):\n",
    "        if not 0 <= k <= self._n:\n",
    "            raise IndexError('invalid index')\n",
    "        return self._A[k]\n",
    "    \n",
    "    def append(self, obj):\n",
    "        if self._n == self._capacity:\n",
    "            self._resize(2 * self._capacity)\n",
    "        self._A[self._n] = obj;\n",
    "        self._n += 1\n",
    "        \n",
    "    def _resize(self, c):\n",
    "        B = self._make_array(c)\n",
    "        for k in range(self._n):\n",
    "            B[k] = self._A[k]\n",
    "        self._A = B\n",
    "        self._capacity = c\n",
    "        \n",
    "    def _make_array(self, c):\n",
    "        return (c * ctypes.py_object)()\n",
    "    "
   ]
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   "execution_count": null,
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