python_underscore.ipynb

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   "source": [
    "# Underscore"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Python Interpreter"
   ]
  },
  {
   "cell_type": "code",
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   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "''"
      ]
     },
     "execution_count": 1,
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   ],
   "source": [
    ">>> 10\n",
    ">>> _*30"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Ignore Value"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1 3\n",
      "1 5\n",
      "a\n",
      "b\n",
      "c\n"
     ]
    }
   ],
   "source": [
    "# Ignore a value when unpacking\n",
    "x, _, y = (1, 2, 3) # x = 1, y = 3 \n",
    "print(x, y)\n",
    "# Ignore the multiple values. It is called \"Extended Unpacking\" which is available in only Python 3.x\n",
    "x, *_, y = (1, 2, 3, 4, 5) # x = 1, y = 5 \n",
    "print(x, y)\n",
    "# ignore in enumerate\n",
    "ignoreList = ['a', 'b', 'c']\n",
    "\n",
    "for _, i in enumerate(ignoreList):\n",
    "    print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Private Variables and Functions"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_single\\_leading\\_underscore\n",
    "- From PEP-8 : \n",
    "_single_leading_underscore: weak \"internal use\" indicator. E.g. from M import * does not import objects whose name starts with an underscore.\n",
    "\n",
    "- private method of class"
   ]
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   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "_version = '1.0'\n",
    "\n",
    "class _ball():\n",
    "    _PI = 3.14\n",
    "    \n",
    "    def __init(self, radius):\n",
    "        self._radius = radius\n",
    "    \n",
    "    def getArea(self):\n",
    "        return self._calculate\n",
    "    \n",
    "    def _calculate(self):\n",
    "        return self._radius^2*_PI\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### single\\_trailing\\_underscore\\_\n",
    "- To avoid conflict Python keywords"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'getListObject' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-4-af3e6c6b657b>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mlist_\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mgetListObject\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m: name 'getListObject' is not defined"
     ]
    }
   ],
   "source": [
    "list_ = getListObject()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_double\\_leading\\_underscore\n",
    "- double underscore will mangle the attribute names of a class to avoid conflicts of attribute names between classes. (Namespace)\n",
    "- _ClassName__method"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class _myPy1:\n",
    "\tdef __init__(self):\n",
    "\t\tprint('my first python myPy1')\n",
    "class myPy:\n",
    "\tdef __init__(self):\n",
    "\t\tprint('my first python myPy')\n",
    "\tdef __method(self):\n",
    "\t\tprint('method in class myPy')\n",
    "\n",
    "myPy()._myPy__method()\n",
    "_myPy1()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_double\\_leading\\_and\\_trailing\\_underscore\\_\\_\n",
    "- This convention is used for special variables or methods (so-called “magic method”) such as__init__, __len__. These methods provides special syntactic features or does special things.\n",
    "- __file__ indicates the location of Python file"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "if __name__ == \"__main__\":\n",
    "    print('hi')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Reference \n",
    "https://hackernoon.com/understanding-the-underscore-of-python-309d1a029edc"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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