Ch2_PythonicCode.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Chapter 2. 파이썬스러운(pythonic) 코드\n",
    "+ 이 장의 목표\n",
    "    + 인덱스와 슬라이스를 이해하고 인덱싱 가능한 객체를 올바른 방식으로 구현\n",
    "    + 시퀀스와 이터러블 구현\n",
    "    + 매직 메서드를 사요해 보다 관용적인 코드 구현\n",
    "    + 부작용을 유발하는 흔한 실수 피하기"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 인덱스와 슬라이스"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "음수 인덱스: 9 5\n",
      "slice 1: (3, 9)\n",
      "slice 2: (4, 5, 3)\n",
      "slice 3: (9,)\n",
      "slice 4: (9, 3, 5, 4)\n",
      "\n",
      "\n",
      "slice index: (5, 9)\n",
      "slice object: (5, 9)\n",
      "\n",
      "\n",
      "slice object vs index: True\n"
     ]
    }
   ],
   "source": [
    "my_numbers = (4, 5, 3, 9)\n",
    "\n",
    "print(\"음수 인덱스:\", my_numbers[-1], my_numbers[-3])\n",
    "print(\"slice 1:\", my_numbers[2:5])\n",
    "print(\"slice 2:\", my_numbers[:3])\n",
    "print(\"slice 3:\", my_numbers[3:])\n",
    "print(\"slice 4:\", my_numbers[::-1])\n",
    "\n",
    "print(\"\\n\")\n",
    "print(\"slice index:\", my_numbers[1:7:2])\n",
    "print(\"slice object:\", my_numbers[slice(1, 7, 2)])\n",
    "\n",
    "print(\"\\n\")\n",
    "interval = slice(None, 3)\n",
    "print(\"slice object vs index:\", my_numbers[interval] == my_numbers[:3])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 자체 시퀀스 생성\n",
    "+ 범위로 인덱싱하는 결과는 해당 클래스와 같은 타입의 인스턴스여아 한다.\n",
    "+ slice에 의해 제공된 범위는 파이썬이 하는 것처럼 마지막 요소는 제외한다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" list wrapping 사례 \"\"\"\n",
    "\n",
    "class Item:\n",
    "    def __init__(self, *values):\n",
    "        self._value = list(values)\n",
    "    \n",
    "    def __len__(self):\n",
    "        return len(self._value)\n",
    "\n",
    "    def __getitem__(self, index):\n",
    "        return self._value.__getitem__(index)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3\n",
      "[4, 5]\n",
      "<class 'list'>\n"
     ]
    }
   ],
   "source": [
    "item = Item(3, 4, 5)\n",
    "print(len(item))\n",
    "print(item[1:])\n",
    "print(type(item[1:]))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 컨텍스트 관리자\n",
    "+ __enter__와 __exit__ 두 개의 매직 메서드로 구성됨\n",
    "+ with 문은 __enter__ 메서드를 호추랗고 이 메서드가 무엇을 반환하든 as 이후에 지정된 변수에 할당됨\n",
    "+ 해당 블록에 대한 마지막 문장이 끝나면 컨텍스트가 종료되며 __exit__ 메서드를 호출함\n",
    "+ 블록 내에 예외 또는 오류가 있는 경우에도 __exit__ 메서드가 여전히 호출되며, 예외는 파라미터로 확인 가능\n",
    "    + True를 반환하면 잠재적으로 발생한 예외를 호출자에게 전파하지 않고 정지함을 의미하나 좋지 않은 습관임"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "systemctl stop postgresql.service\n",
      "pg_dump database\n",
      "systemctl start postgresql.service\n"
     ]
    }
   ],
   "source": [
    "\"\"\" 컨텍스트 관리자를 활용한 DB Dump 사례 \"\"\"\n",
    "\n",
    "def stop_database():\n",
    "    print(\"systemctl stop postgresql.service\")\n",
    "\n",
    "def start_database():\n",
    "    print(\"systemctl start postgresql.service\")\n",
    "\n",
    "\n",
    "class DBHandler:\n",
    "    def __enter__(self):\n",
    "        stop_database()\n",
    "        return self\n",
    "\n",
    "    def __exit__(self, exc_type, ex_value, ex_traceback):\n",
    "        start_database()\n",
    "\n",
    "\n",
    "def db_backup():\n",
    "    print(\"pg_dump database\")\n",
    "\n",
    "def main():\n",
    "    with DBHandler():\n",
    "        db_backup()\n",
    "\n",
    "main()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 컨텍스트 관리자 구현\n",
    "+ contextlib 모듈을 활용한 컨텍스트 관리자 구현 가능\n",
    "    + contextlib.contextmanager 데코레이터를 적용하면 해당 함수의 코드를 컨텍스트 관리자로 변환함\n",
    "    + contextlib.ContextDecorator 를 사용하면 with문 없이 완전히 독립적인 실행가능\n",
    "        + 컨텍스트 관리자 내부에서 사용하고자 하는 객체를 얻을 수 없는 단점\n",
    "        + e.g.) with offline_back() as bp: 처럼 사용할 수 없음\n",
    "    + with contextlib.suppress(DataConversionException) 은 로직 자체적으로 처리하고 있음을 예외임을 명시하고 실패하지 않도록 함"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "systemctl stop postgresql.service\n",
      "pg_dump database\n",
      "systemctl start postgresql.service\n"
     ]
    }
   ],
   "source": [
    "import contextlib\n",
    "\n",
    "@contextlib.contextmanager\n",
    "def db_handler():\n",
    "    stop_database()\n",
    "    yield\n",
    "    start_database()\n",
    "\n",
    "def main():\n",
    "    with db_handler():\n",
    "        db_backup()\n",
    "\n",
    "main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [],
   "source": [
    "import contextlib\n",
    "\n",
    "class dbhandler_decorator(contextlib.ContextDecorator):\n",
    "    def __enter__(self):\n",
    "        stop_database()\n",
    "\n",
    "    def __exit__(self, ext_type, ex_value, ex_traceback):\n",
    "        start_database()\n",
    "\n",
    "@dbhandler_decorator()\n",
    "def offline_backup():\n",
    "    print(\"pg_dump database\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 프로퍼티, 속성과 객체 메서드의 다른 타입들\n",
    "\n",
    "+ 파이썬 객체의 모든 프로퍼티와 함수는 public\n",
    "+ 따라서 엄격한 강제사항은 없지만 밑줄로 시작하는 속성은 해당 객체에 대해 private을 의미하며 외부에서 호출하지 않기를 기대함\n",
    "\n",
    "### 파이썬에서의 밑줄\n",
    "+ 이중 밑줄은 여러 번 확장되는 클래스의 메서드를 이름 충돌 없이 오버라이드하기 위해 만들어짐\n",
    "+ 이중 밑줄이 아닌 하나의 밑줄을 사용하는 파이썬의 관습을 지킬 것\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'source': 'postgresql://localhost', '_timeout': 70}\n"
     ]
    }
   ],
   "source": [
    "class Connector:\n",
    "    def __init__(self, source):\n",
    "        self.source = source\n",
    "        self._timeout = 60 # 하나의 밑줄\n",
    "\n",
    "conn = Connector(\"postgresql://localhost\")\n",
    "\n",
    "conn._timeout = 70\n",
    "print(conn.__dict__)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'Connector' object has no attribute '__timeout'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-8-bd7c24031309>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      6\u001b[0m \u001b[0mconn\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mConnector\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"postgresql://localhost\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      7\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 8\u001b[0;31m \u001b[0mconn\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m__timeout\u001b[0m \u001b[0;31m# \"접근할 수 없다\"가 아닌 \"존재하지 않는다\"는 오류 발생\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: 'Connector' object has no attribute '__timeout'"
     ]
    }
   ],
   "source": [
    "class Connector:\n",
    "    def __init__(self, source):\n",
    "        self.source = source\n",
    "        self.__timeout = 60 # 두 개의 밑줄\n",
    "\n",
    "conn = Connector(\"postgresql://localhost\")\n",
    "\n",
    "conn.__timeout # \"접근할 수 없다\"가 아닌 \"존재하지 않는다\"는 오류 발생"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'source': 'postgresql://localhost', '_Connector__timeout': 80}\n"
     ]
    }
   ],
   "source": [
    "conn._Connector__timeout = 80 # 이름이 바뀌어 있음\n",
    "print(conn.__dict__)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 프로퍼티\n",
    "\n",
    "+ 객체의 어떤 속성에 대한 접근을 제어하려는 경우 사용함 (잘못된 정보의 입력 제한 등)\n",
    "+ 모든 속성에\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "유효한 이메일이 아니므로 shyeon.kang@ 값을 사용할 수 없음",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-10-d5bfb8fe6f01>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m     22\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     23\u001b[0m \u001b[0muser\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mUser\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"shyeon.kang\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 24\u001b[0;31m \u001b[0muser\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0memail\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m\"shyeon.kang@\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-10-d5bfb8fe6f01>\u001b[0m in \u001b[0;36memail\u001b[0;34m(self, new_email)\u001b[0m\n\u001b[1;32m     18\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0memail\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mnew_email\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     19\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0;32mnot\u001b[0m \u001b[0mis_valid_email\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mnew_email\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 20\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mValueError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34mf\"유효한 이메일이 아니므로 {new_email} 값을 사용할 수 없음\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     21\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_email\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mnew_email\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     22\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: 유효한 이메일이 아니므로 shyeon.kang@ 값을 사용할 수 없음"
     ]
    }
   ],
   "source": [
    "import re\n",
    "\n",
    "EMAIL_FORMAT = re.compile(r\"[^@]+@[^@]+[^@]+\")\n",
    "\n",
    "def is_valid_email(potentially_valid_email: str):\n",
    "    return re.match(EMAIL_FORMAT, potentially_valid_email) is not None\n",
    "\n",
    "class User:\n",
    "    def __init__(self, username):\n",
    "        self.username = username\n",
    "        self._email = None\n",
    "\n",
    "    @property\n",
    "    def email(self):\n",
    "        return self._email\n",
    "\n",
    "    @email.setter\n",
    "    def email(self, new_email):\n",
    "        if not is_valid_email(new_email):\n",
    "            raise ValueError(f\"유효한 이메일이 아니므로 {new_email} 값을 사용할 수 없음\")\n",
    "        self._email = new_email\n",
    "\n",
    "user = User(\"shyeon.kang\")\n",
    "user.email = \"shyeon.kang@\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [],
   "source": [
    "user = User(\"Kang Seonghyeon\")\n",
    "user.email = \"Seonghyeon@gmail.com\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 이터러블 객체\n",
    "+ 반복 가능한지 확인하기 위해 파이썬은 고수준에서 다음 두 가지를 차례로 검사\n",
    "    + 객체가 __next__나 __iter__ 이터레이터 메스드 중 하나를 포함하는지 여부\n",
    "    + 객체가 시퀀스이고 __len__과 __getitem__을 모두 가졌는지 여부\n",
    "\n",
    "### 이터러블 객체 만들기\n",
    "+ 객체를 반복하려고 하면 파이썬은 해당 객체의 iter() 함수를 호출\n",
    "+ for 문은 StopIteration 예외가 발생할 때까지 next()를 호출하는 것과 같음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2019-01-01\n",
      "2019-01-02\n",
      "2019-01-03\n",
      "2019-01-04\n"
     ]
    }
   ],
   "source": [
    "from datetime import timedelta\n",
    "from datetime import date\n",
    "\n",
    "class DateRangeIterable:\n",
    "    \"\"\" 자체 이터레이터 메서드를 가지고 있음 \"\"\"\n",
    "\n",
    "    def __init__(self, start_date, end_date):\n",
    "        self.start_date = start_date\n",
    "        self.end_date = end_date\n",
    "        self._present_day = start_date\n",
    "\n",
    "    def __iter__(self):\n",
    "        return self # 자신이 이터러블임을 나타냄\n",
    "\n",
    "    def __next__(self):\n",
    "        if self._present_day >= self.end_date:\n",
    "            raise StopIteration\n",
    "        today = self._present_day\n",
    "        self._present_day += timedelta(days=1)\n",
    "        return today\n",
    "\n",
    "for day in DateRangeIterable(date(2019, 1, 1), date(2019, 1, 5)):\n",
    "    print(day)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "+ for 문은 StopIteration 예외가 발생할 때까지 next()를 호출하는 것과 같음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [],
   "source": [
    "r = DateRangeIterable(date(2019, 1, 1), date(2019, 1, 5))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(datetime.date(2019, 1, 1),\n",
       " datetime.date(2019, 1, 2),\n",
       " datetime.date(2019, 1, 3),\n",
       " datetime.date(2019, 1, 4))"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "next(r), next(r), next(r), next(r)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "ename": "StopIteration",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mStopIteration\u001b[0m                             Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-15-8ebe59a56b1d>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mnext\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mr\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-12-3e5c429f856d>\u001b[0m in \u001b[0;36m__next__\u001b[0;34m(self)\u001b[0m\n\u001b[1;32m     15\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__next__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     16\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_present_day\u001b[0m \u001b[0;34m>=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mend_date\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 17\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mStopIteration\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     18\u001b[0m         \u001b[0mtoday\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_present_day\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     19\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_present_day\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0mtimedelta\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mdays\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mStopIteration\u001b[0m: "
     ]
    }
   ],
   "source": [
    "next(r)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "+ 한 번 실행하면 끝의 날짜에 도달한상태이므로 이후에 호출하면 계속 StopIteration 예외가 발행하는 문제\n",
    "+ 제너레이터를 사용하면 이러한 문제를 해결할 수 있음(<b>컨테이너 이터러블</b>이라고 함)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'2019-01-01, 2019-01-02, 2019-01-03, 2019-01-04'"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "r1 = DateRangeIterable(date(2019, 1, 1), date(2019, 1, 5))\n",
    "\", \".join(map(str, r1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "max() arg is an empty sequence",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-17-4544ff45dc14>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mmax\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mr1\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m: max() arg is an empty sequence"
     ]
    }
   ],
   "source": [
    "max(r1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 컨테이너 이터러블 적용 \"\"\"\n",
    "\n",
    "class DateRangeIterable:\n",
    "    \"\"\" 자체 이터레이터 메서드를 가지고 있음 \"\"\"\n",
    "\n",
    "    def __init__(self, start_date, end_date):\n",
    "        self.start_date = start_date\n",
    "        self.end_date = end_date\n",
    "        self._present_day = start_date\n",
    "\n",
    "    def __iter__(self):\n",
    "        current_day = self.start_date\n",
    "        while current_day < self.end_date:\n",
    "            yield current_day\n",
    "            current_day += timedelta(days=1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'2019-01-01, 2019-01-02, 2019-01-03, 2019-01-04'"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "r1 = DateRangeIterable(date(2019, 1, 1), date(2019, 1, 5))\n",
    "\", \".join(map(str, r1))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "datetime.date(2019, 1, 4)"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "max(r1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 시퀀스 만들기\n",
    "+ 이터러블은 메모리를 적게 사용하지만 n번째 요소를 얻기 위한 시각복잡도는 O(n)이다.\n",
    "+ 시퀀스로 구현하면 더 많은 메모리가 사용되지만(모든 것을 보관해야 하므로) 특정 요소를 가져오기 위한 인덱싱 시간복잡도는 O(1)로 상수에 가능하다."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [],
   "source": [
    "class DateRangeSequence:\n",
    "    def __init__(self, start_date, end_date):\n",
    "        self.start_date = start_date\n",
    "        self.end_date = end_date\n",
    "        self._range = self._create_range()\n",
    "\n",
    "    def _create_range(self):\n",
    "        days = []\n",
    "        current_day = self.start_date\n",
    "        while current_day < self.end_date:\n",
    "            days.append(current_day)\n",
    "            current_day += timedelta(days=1)\n",
    "        return days\n",
    "\n",
    "    def __getitem__(self, day_no):\n",
    "        return self._range[day_no]\n",
    "\n",
    "    def __len__(self):\n",
    "        return len(self._range)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2019-01-01\n",
      "2019-01-02\n",
      "2019-01-03\n",
      "2019-01-04\n"
     ]
    }
   ],
   "source": [
    "s1 = DateRangeSequence(date(2019, 1, 1), date(2019, 1, 5))\n",
    "for day in s1:\n",
    "    print(day)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(datetime.date(2019, 1, 1),\n",
       " datetime.date(2019, 1, 4),\n",
       " datetime.date(2019, 1, 4))"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s1[0], s1[3], s1[-1]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 컨테이너 객체\n",
    "\n",
    "+ 컨테이너는 __contain__메서드를 구현한 객체임\n",
    "+ 일반적으로 Boolean을 반환하며 in 키워드가 발견될 때 호출됨\n",
    "    + element in container ==> container.__contains__(element)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Boundaries:\n",
    "    def __init__(self, width, height):\n",
    "        self.width = width\n",
    "        self.height = height\n",
    "\n",
    "    def __contains__(self, coord):\n",
    "        x, y = coord\n",
    "        return 0 <=x < self.width and 0 <= y < self.height\n",
    "    \n",
    "class Grid:\n",
    "    def __init__(self, width, height):\n",
    "        self.width = width\n",
    "        self.height = height\n",
    "        self.limits = Boundaries(width, height)\n",
    "\n",
    "    def __contains__(self, coord):\n",
    "        return coord in self.limits\n",
    "\n",
    "def mark_coordiante(grid, coord):\n",
    "    if coord in grid:\n",
    "        print(f\"{coord} is in limit\")\n",
    "    else:\n",
    "        print(f\"{coord} is out of the limit\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(3, 4) is in limit\n"
     ]
    }
   ],
   "source": [
    "grid = Grid(4, 5)\n",
    "\n",
    "coord = (3, 4)\n",
    "mark_coordiante(grid, coord)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(5, 7) is out of the limit\n"
     ]
    }
   ],
   "source": [
    "grid = Grid(4, 5)\n",
    "\n",
    "coord = (5, 7)\n",
    "mark_coordiante(grid, coord)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 객체의 동적인 속성\n",
    "\n",
    "+ 파이썬은 객체를 호출하면 객체 사전에서 <myattribute>를 찾아서 __getattribute__를 호출\n",
    "+ 객체에 찾고 있는 속성이 없는 경우 객체 이름을 파라미터로 __getattr__ 이라는 추가 메서드가 호출됨"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "class DynamicAttribute:\n",
    "    def __init__(self, attribute):\n",
    "        self.attribute = attribute\n",
    "\n",
    "    def __getattr__(self, attr):\n",
    "        if attr.startswith(\"fallback_\"):\n",
    "            name = attr.replace(\"fallback_\", \"\")\n",
    "            return f\"[fallback resolved] {name}\"\n",
    "        raise AttributeError(f\"{self.__class__.__name__}에는 {attr} 속성이 없음\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'value'"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dyn = DynamicAttribute(\"value\")\n",
    "dyn.attribute"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[fallback resolved] test'"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dyn.fallback_test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'new value'"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dyn.__dict__[\"fallback_new\"] = \"new value\"\n",
    "dyn.fallback_new"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'default'"
      ]
     },
     "execution_count": 31,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "getattr(dyn, \"something\", \"default\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'new value'"
      ]
     },
     "execution_count": 32,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "getattr(dyn, \"fallback_new\", \"default\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "DynamicAttribute에는 something 속성이 없음",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-33-85abb70e4746>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mdyn\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msomething\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-27-25fec96d92ea>\u001b[0m in \u001b[0;36m__getattr__\u001b[0;34m(self, attr)\u001b[0m\n\u001b[1;32m      7\u001b[0m             \u001b[0mname\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mattr\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mreplace\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"fallback_\"\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m\"\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      8\u001b[0m             \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"[fallback resolved] {name}\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 9\u001b[0;31m         \u001b[0;32mraise\u001b[0m \u001b[0mAttributeError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34mf\"{self.__class__.__name__}에는 {attr} 속성이 없음\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: DynamicAttribute에는 something 속성이 없음"
     ]
    }
   ],
   "source": [
    "dyn.something"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 호출형(callable) 객체\n",
    "+ __call__을 사용하면 객체를 일반 함수처럼 호출할 수 있음\n",
    "+ 여기에 전달된 모든 파라미터는 __call__ 메서드에 그대로 전달됨"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import defaultdict\n",
    "\n",
    "class CallCount:\n",
    "    def __init__(self):\n",
    "        self._counts = defaultdict(int)\n",
    "\n",
    "    def __call__(self, argument):\n",
    "        self._counts[argument] += 1\n",
    "        return self._counts[argument]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1\n",
      "1\n",
      "2\n",
      "2\n"
     ]
    }
   ],
   "source": [
    "cc = CallCount()\n",
    "print(cc(1))\n",
    "print(cc(2))\n",
    "print(cc(2))\n",
    "print(cc(1))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 파이썬에서 유의할 점\n",
    "\n",
    "### 변경 가능한 파라미터의 기본 값\n",
    "+ 변경 가능한 객체를 함수의 기본 인자로 사용하면 안됨"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [],
   "source": [
    "def wrong_user_display(user_metadata: dict = {\"name\":\"John\", \"age\":30}):\n",
    "    name = user_metadata.pop(\"name\")\n",
    "    age = user_metadata.pop(\"age\")\n",
    "    return f\"{name} ({age})\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'John (30)'"
      ]
     },
     "execution_count": 37,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "wrong_user_display()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'kang (20)'"
      ]
     },
     "execution_count": 38,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "wrong_user_display({\"name\":\"kang\", \"age\":20})"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 39,
   "metadata": {},
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "'name'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-39-468f5f73dd28>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mwrong_user_display\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-36-cb8e54b62070>\u001b[0m in \u001b[0;36mwrong_user_display\u001b[0;34m(user_metadata)\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mwrong_user_display\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0muser_metadata\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mdict\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m{\u001b[0m\u001b[0;34m\"name\"\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\"John\"\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m\"age\"\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;36m30\u001b[0m\u001b[0;34m}\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m     \u001b[0mname\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"name\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      3\u001b[0m     \u001b[0mage\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"age\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m     \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"{name} ({age})\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mKeyError\u001b[0m: 'name'"
     ]
    }
   ],
   "source": [
    "wrong_user_display()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 61,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 함수 내로 기본값 설정 \"\"\"\n",
    "def good_user_display(user = None):\n",
    "    user_metadata = {\"name\":\"John\", \"age\":30} # 기본값?\n",
    "\n",
    "    def display(user_metadata = user_metadata):\n",
    "        name = user_metadata.pop(\"name\")\n",
    "        age = user_metadata.pop(\"age\")\n",
    "        return f\"{name} ({age})\"\n",
    "\n",
    "    return display(user)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 62,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'NoneType' object has no attribute 'pop'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-62-aa065ba4fa22>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mgood_user_display\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-61-6748388d2539>\u001b[0m in \u001b[0;36mgood_user_display\u001b[0;34m(user)\u001b[0m\n\u001b[1;32m      8\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"{name} ({age})\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      9\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 10\u001b[0;31m     \u001b[0;32mreturn\u001b[0m \u001b[0mdisplay\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0muser\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-61-6748388d2539>\u001b[0m in \u001b[0;36mdisplay\u001b[0;34m(user_metadata)\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mdisplay\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0muser_metadata\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 6\u001b[0;31m         \u001b[0mname\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"name\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      7\u001b[0m         \u001b[0mage\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"age\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      8\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"{name} ({age})\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mAttributeError\u001b[0m: 'NoneType' object has no attribute 'pop'"
     ]
    }
   ],
   "source": [
    "good_user_display()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 57,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'kang (20)'"
      ]
     },
     "execution_count": 57,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "good_user_display({\"name\":\"kang\", \"age\":20})"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 58,
   "metadata": {},
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'NoneType' object has no attribute 'pop'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-58-aa065ba4fa22>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mgood_user_display\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-55-6748388d2539>\u001b[0m in \u001b[0;36mgood_user_display\u001b[0;34m(user)\u001b[0m\n\u001b[1;32m      8\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"{name} ({age})\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      9\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 10\u001b[0;31m     \u001b[0;32mreturn\u001b[0m \u001b[0mdisplay\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0muser\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-55-6748388d2539>\u001b[0m in \u001b[0;36mdisplay\u001b[0;34m(user_metadata)\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mdisplay\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0muser_metadata\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 6\u001b[0;31m         \u001b[0mname\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"name\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      7\u001b[0m         \u001b[0mage\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0muser_metadata\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mpop\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"age\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      8\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0;34mf\"{name} ({age})\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mAttributeError\u001b[0m: 'NoneType' object has no attribute 'pop'"
     ]
    }
   ],
   "source": [
    "good_user_display()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 내장(built-in) 타입 확장\n",
    "\n",
    "+ 리스트, 문자열, 사전과 같은 내장 타입을 확장하는 올바른 방법은 collections 모듈을 사용하는 것\n",
    "+ 내장 함수에서 override가 동작하지 않음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 44,
   "metadata": {},
   "outputs": [],
   "source": [
    "class BadList(list):\n",
    "    def __getitem__(self, index):\n",
    "        value = super().__getitem__(index)\n",
    "        if index % 2 == 0:\n",
    "            prefix = \"even\"\n",
    "        else:\n",
    "            prefix = \"odd\"\n",
    "        return f\"[{prefix}] {value}  \""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 45,
   "metadata": {},
   "outputs": [],
   "source": [
    "bl = BadList((0, 1, 2, 3, 4, 5))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[even] 0  '"
      ]
     },
     "execution_count": 46,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bl[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[odd] 1  '"
      ]
     },
     "execution_count": 47,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bl[1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "sequence item 0: expected str instance, int found",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-48-dd153dfa9cd1>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;34m\"\"\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mjoin\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mbl\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# join() 내부의 __getitem__ 함수가 호출되지 않음\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: sequence item 0: expected str instance, int found"
     ]
    }
   ],
   "source": [
    "\"\".join(bl) # join() 내부의 __getitem__ 함수가 호출되지 않음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" collections 모듈을 사용하여 문제 해결 \"\"\"\n",
    "\n",
    "from collections import UserList\n",
    "\n",
    "class GoodList(UserList):\n",
    "    def __getitem__(self, index):\n",
    "        value = super().__getitem__(index)\n",
    "        if index % 2 == 0:\n",
    "            prefix = \"even\"\n",
    "        else:\n",
    "            prefix = \"odd\"\n",
    "        return f\"[{prefix}] {value}  \""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 50,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[even] 0  [odd] 1  [even] 2  [odd] 3  [even] 4  [odd] 5  '"
      ]
     },
     "execution_count": 50,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "bl = GoodList((0, 1, 2, 3, 4, 5))\n",
    "\"\".join(bl)"
   ]
  }
 ],
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