{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 파이썬의 클래스 구조"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## class 키워드를 사용한 클래스 정의"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Page:  # 클래스 정의\n",
    "    def __init__(self, num, content):\n",
    "        self.num = num  # ページ番号\n",
    "        self.content = content  # 페이지 내용\n",
    "    def output(self):\n",
    "        return f'{self.content}'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "__main__.Page"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Page  # 클래스 객체 Page가 정의됨"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 인스턴스 만들기"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 인스턴스화\n",
    "title_page = Page(0, 'Python Practice Book')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "__main__.Page"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "type(title_page)  # 인스턴스의 클래스를 확인함"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Page 클래스의 인스턴스인지 확인함\n",
    "isinstance(title_page, Page)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['__class__',\n",
       " '__delattr__',\n",
       " '__dict__',\n",
       " '__dir__',\n",
       " '__doc__',\n",
       " '__eq__',\n",
       " '__format__',\n",
       " '__ge__',\n",
       " '__getattribute__',\n",
       " '__gt__',\n",
       " '__hash__',\n",
       " '__init__',\n",
       " '__init_subclass__',\n",
       " '__le__',\n",
       " '__lt__',\n",
       " '__module__',\n",
       " '__ne__',\n",
       " '__new__',\n",
       " '__reduce__',\n",
       " '__reduce_ex__',\n",
       " '__repr__',\n",
       " '__setattr__',\n",
       " '__sizeof__',\n",
       " '__str__',\n",
       " '__subclasshook__',\n",
       " '__weakref__',\n",
       " 'content',\n",
       " 'num',\n",
       " 'output']"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 인스턴스가 가진 속성을 확인함\n",
    "dir(title_page)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 인스턴스 ── 클래스를 기반으로 만들어진 객체"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 인스턴스 메서드 ── 인스턴스에 묶인 메서드"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "title_page.output()  # 인스턴스 메서드 호출"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### 메서드 객채와 함수 객체"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Klass:\n",
    "    def some_method(self):  # 인스턴스 메서드 정의\n",
    "        print('method')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "def some_function(self):  # 같은 인수의 함수 정의\n",
    "    print('function')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "function"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 함수는 function 클래스의 인스턴스임\n",
    "type(some_function)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "function"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 인스턴스 메서드도 function 클래스의 인스턴스\n",
    "type(Klass.some_method)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "method"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 인스턴스를 통해 접근하면 method 클래스가 됨\n",
    "kls = Klass()\n",
    "type(kls.some_method)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 클래스 객체의 속성에 함수를 추가\n",
    "Klass.some_function = some_function"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "function\n"
     ]
    }
   ],
   "source": [
    "# 인스턴스 메서드로 실행\n",
    "kls.some_function()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 인스턴스 변수 ── 인스턴스가 저장하는 변수"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "title_page.section = 0\n",
    "title_page.section"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'Page' object has no attribute 'section'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-16-622c9b4a10cc>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mfirst_page\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mPage\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m'first page'\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[0mfirst_page\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msection\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: 'Page' object has no attribute 'section'"
     ]
    }
   ],
   "source": [
    "first_page = Page(1, 'first page')\n",
    "first_page.section"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 인스턴스 초기화"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_init\\_\\_() ── 인스턴스 초기화를 수행하는 특수 메서드"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 클래스 정의 \n",
    "class Page:\n",
    "    def __init__(self, num, content, section=None):\n",
    "        self.num = num\n",
    "        self.content = content\n",
    "        self.section = section\n",
    "    def output(self):\n",
    "        return f'{self.content}'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 인수를 전달해 인스턴스화 하기"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 인스턴스 작성\n",
    "title_page = Page(0, 'Python Practice Book')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [],
   "source": [
    "title_page.section  # section은 None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "title_page.output()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [],
   "source": [
    "# section을 지정해 다른 인스턴스를 작성\n",
    "first_page = Page(1, 'first page', 1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first_page.section  # section이 지정되어 있음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'first page'"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first_page.output()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_init\\_\\_()과 \\_\\_new\\_\\_()의 차이 ── 이니셜라이저와 컨스트럭터"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Klass:\n",
    "    def __new__(cls, *args):  # 컨스트럭터\n",
    "        print(f'{cls=}')\n",
    "        print('new', args)\n",
    "        # 작성한 인스터스를 반환함 \n",
    "        return super().__new__(cls)\n",
    "    def __init__(self, *args): # 이니셜라이저\n",
    "        # 인스턴스 초기화는 여기에서 수행함\n",
    "        print('init', args)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "cls=<class '__main__.Klass'>\n",
      "new (1, 2, 3)\n",
      "init (1, 2, 3)\n"
     ]
    }
   ],
   "source": [
    "# 인스턴스화\n",
    "kls = Klass(1, 2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_new\\_\\_() 사용 시 주의점"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Evil:\n",
    "    def __new__(cls, *args):\n",
    "        return 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Evil 클래스 인스턴스화\n",
    "evil = Evil()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "isinstance(evil, Evil)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "int"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "type(evil)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 인스턴스는 __new__()의 반환값\n",
    "evil"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [],
   "source": [
    "class MyClass(Evil):\n",
    "    def print_class(self):\n",
    "        print('MyClass')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [],
   "source": [
    "my = MyClass()  # my 값은 1이 됨"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'int' object has no attribute 'print_class'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-33-5c63bdce6f16>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;31m# 추가되었어야 할 메서드를 이용할 수 없음\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[0mmy\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mprint_class\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;31mAttributeError\u001b[0m: 'int' object has no attribute 'print_class'"
     ]
    }
   ],
   "source": [
    "# 추가되었어야 할 메서드를 이용할 수 없음\n",
    "my.print_class()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1"
      ]
     },
     "execution_count": 34,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 프로퍼티 ── 인스턴스 메서드를 인스턴스 변수와 같이 다룸"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Book:\n",
    "    def __init__(self, raw_price):\n",
    "        if raw_price < 0:\n",
    "            raise ValueError('price must be positive')\n",
    "        self.raw_price = raw_price\n",
    "        self._discounts = 0\n",
    "    @property\n",
    "    def discounts(self):\n",
    "        return self._discounts\n",
    "    @discounts.setter\n",
    "    def discounts(self, value):\n",
    "        if value < 0 or 100 < value:\n",
    "            raise ValueError(\n",
    "                'discounts must be between 0 and 100')\n",
    "        self._discounts = value\n",
    "    @property\n",
    "    def price(self):\n",
    "        multi = 100 - self._discounts\n",
    "        return int(self.raw_price * multi / 100)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0"
      ]
     },
     "execution_count": 36,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "book = Book(2000)\n",
    "book.discounts  # 초기 할인율 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "2000"
      ]
     },
     "execution_count": 37,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "book.price  # 초기 가격 2000"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "1600"
      ]
     },
     "execution_count": 38,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "book.discounts = 20  # 할인율 설정\n",
    "book.price  # 할인 후의 가격"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 39,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "discounts must be between 0 and 100",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-39-4bc99df62c28>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mbook\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdiscounts\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;36m120\u001b[0m  \u001b[0;31m# 할인율이 100을 초과하면 에러 발생\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-35-553c66fea917>\u001b[0m in \u001b[0;36mdiscounts\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     11\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mdiscounts\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\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     12\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mvalue\u001b[0m \u001b[0;34m<\u001b[0m \u001b[0;36m0\u001b[0m \u001b[0;32mor\u001b[0m \u001b[0;36m100\u001b[0m \u001b[0;34m<\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 13\u001b[0;31m             raise ValueError(\n\u001b[0m\u001b[1;32m     14\u001b[0m                 'discounts must be between 0 and 100')\n\u001b[1;32m     15\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_discounts\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: discounts must be between 0 and 100"
     ]
    }
   ],
   "source": [
    "book.discounts = 120  # 할인율이 100을 초과하면 에러 발생"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### property ── 값을 얻을 때 호출되는 메서드"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### setter ── 값을 설정할 때 호출되는 메서드"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 40,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "discounts must be between 0 and 100",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-40-1a951ff04058>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mbook\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdiscounts\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m-\u001b[0m\u001b[0;36m20\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-35-553c66fea917>\u001b[0m in \u001b[0;36mdiscounts\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     11\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mdiscounts\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\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     12\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0mvalue\u001b[0m \u001b[0;34m<\u001b[0m \u001b[0;36m0\u001b[0m \u001b[0;32mor\u001b[0m \u001b[0;36m100\u001b[0m \u001b[0;34m<\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 13\u001b[0;31m             raise ValueError(\n\u001b[0m\u001b[1;32m     14\u001b[0m                 'discounts must be between 0 and 100')\n\u001b[1;32m     15\u001b[0m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_discounts\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: discounts must be between 0 and 100"
     ]
    }
   ],
   "source": [
    "book.discounts = -20"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 41,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "can't set attribute",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-41-cd29227d939f>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mbook\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mprice\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;36m1000\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: can't set attribute"
     ]
    }
   ],
   "source": [
    "book.price = 1000"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 클래스와 인스턴스의 프라이빗 속성"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 언더스코어로 시작하는 속성"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 42,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "20"
      ]
     },
     "execution_count": 42,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "book._discounts  # _로 시작하는 변수도 참조할 수 있음"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 언더스코어 2개로 시작하는 속성"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 43,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Klass:\n",
    "    def __init__(self, x):\n",
    "        self.__x = x"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 44,
   "metadata": {
    "tags": [
     "raises-exception"
    ]
   },
   "outputs": [
    {
     "ename": "AttributeError",
     "evalue": "'Klass' object has no attribute '__x'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m                            Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-44-0c02c06d28bb>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mkls\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mKlass\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;36m10\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[0mkls\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m__x\u001b[0m  \u001b[0;31m# 이 이름으로는 참조할 수 없음\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mAttributeError\u001b[0m: 'Klass' object has no attribute '__x'"
     ]
    }
   ],
   "source": [
    "kls = Klass(10)\n",
    "kls.__x  # 이 이름으로는 참조할 수 없음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 45,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 45,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "kls._Klass__x  # 변환 규칙을 알고 있다면 참조할 수 있음"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 프라이빗 속성에 대한 파이썬 커뮤니티의 사상"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 클래스 ── 인스턴스의 모형이 되는 객체"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 클래스 변수 ── 클래스 객체가 유지하는 변수"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 46,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 클래스 변수를 가진 클래스 정의\n",
    "class Page:\n",
    "    book_title = 'Python Practice Book'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 47,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 47,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Page.book_title  # 인스턴스가 없어도 참조할 수 있음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'No title'"
      ]
     },
     "execution_count": 48,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "Page.book_title = 'No title'  # 클래스 변수 업데이트\n",
    "Page.book_title"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 클래스 변수는 인스턴스에서도 참조 가능"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 49,
   "metadata": {},
   "outputs": [],
   "source": [
    "first_page = Page()\n",
    "second_page = Page()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 50,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'No title'"
      ]
     },
     "execution_count": 50,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 클래스 변수는 인스턴스에서도 참조 가능\n",
    "first_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 51,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'No title'"
      ]
     },
     "execution_count": 51,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "second_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 52,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 클래스 변수 업데이트\n",
    "Page.book_title = 'Python Practice Book'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 53,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 53,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 클래스 변수는 모든 인스턴스에서 공유됨\n",
    "first_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 54,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 54,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "second_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 55,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[Draft]Python Practice Book'"
      ]
     },
     "execution_count": 55,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 아래는 인스턴스 변수가 됨\n",
    "first_page.book_title = '[Draft]Python Practice Book'\n",
    "first_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 56,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 클래스 변수는 변경되지 않음\n",
    "Page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 57,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'[Draft]Python Practice Book'"
      ]
     },
     "execution_count": 57,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first_page.book_title  # 인스턴스 변수"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 58,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 인스턴스 변수 삭제\n",
    "del first_page.book_title"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 59,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Python Practice Book'"
      ]
     },
     "execution_count": 59,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 인스턴스 속성이 아니므로, 클래스 속성이 검색됨\n",
    "first_page.book_title"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 클래스 메서드 ── 클래스에 속한 메서드"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 60,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 속성을 이용한 정렬에 사용할 수 있는 표준 라이브러리를 임포트\n",
    "from operator import attrgetter"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 61,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Page:\n",
    "    book_title = 'Python Practice Book'\n",
    "    def __init__(self, num, content):\n",
    "        self.num = num\n",
    "        self.content = content\n",
    "    def output(self):\n",
    "        return f'{self.content}'\n",
    "    # 클래스 메서드의 첫 번째 인수는 클래스 객체\n",
    "    @classmethod\n",
    "    def print_pages(cls, *pages):\n",
    "        # 클래스 객체 이용\n",
    "        print(cls.book_title)\n",
    "        pages = list(pages)\n",
    "        # 페이지 순으로 정렬해서 출력\n",
    "        for page in sorted(pages, key=attrgetter('num')):\n",
    "            print(page.output())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 62,
   "metadata": {},
   "outputs": [],
   "source": [
    "first = Page(1, 'first page')\n",
    "second = Page(2, 'second page')\n",
    "third = Page(3, 'third page')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 63,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Python Practice Book\n",
      "first page\n",
      "second page\n",
      "third page\n"
     ]
    }
   ],
   "source": [
    "# 클래스 메서드 호출\n",
    "Page.print_pages(first, third, second)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 64,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Python Practice Book\n",
      "first page\n",
      "second page\n",
      "third page\n"
     ]
    }
   ],
   "source": [
    "# 인스턴스에서도 호출할 수 있음\n",
    "first.print_pages(first, third, second)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 스태틱 메서드 ── 함수처럼 동작하는 메서드"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 65,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Page:\n",
    "    def __init__(self, num, content):\n",
    "        self.num = num\n",
    "        self.content = content\n",
    "    @staticmethod  # 스태틱 메서드로 정의\n",
    "    def check_blank(page):\n",
    "        return bool(page.content)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 66,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 66,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "page = Page(1, '')\n",
    "Page.check_blank(page)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 67,
   "metadata": {},
   "outputs": [],
   "source": [
    "def check_blank(page):  # 함수로 문제 없음\n",
    "    return bool(page.content)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 68,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 68,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "check_blank(page)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 클래스 상속"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 메서드 오버라이드와 super()를 사용한 베이스 클래스로의 접근"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 69,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Page:\n",
    "    def __init__(self, num, content):\n",
    "        self.num = num\n",
    "        self.content = content\n",
    "    def output(self):\n",
    "        return f'{self.content}'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 70,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 메서드 오버라이드 \n",
    "class TitlePage(Page):\n",
    "    def output(self):\n",
    "        # 베이스 클래스의 메서드는 자동으로 호출되지 않으므로\n",
    "        # 명시적으로 호출함\n",
    "        title = super().output()\n",
    "        return title.upper()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 71,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'PYTHON PRACTICE BOOK'"
      ]
     },
     "execution_count": 71,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "title = TitlePage(0, 'Python Practice Book')\n",
    "title.output()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 모든 객체는 object 클래스의 서브 클래스"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 72,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Length(float):  # 내장 타입의 서브 클래스 작성\n",
    "    def to_cm(self):\n",
    "        return super().__str__() + 'cm'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 73,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "16.0cm\n"
     ]
    }
   ],
   "source": [
    "pencil_length = Length(16)\n",
    "print(pencil_length.to_cm())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 다중 상속 ── 여러 베이스 클래스를 지정"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 74,
   "metadata": {},
   "outputs": [],
   "source": [
    "class HTMLPageMixin:\n",
    "    def to_html(self):\n",
    "        return f'<html><body>{self.output()}</body></html>'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 75,
   "metadata": {},
   "outputs": [],
   "source": [
    "# 다중 상속을 사용한 Mixin 이용\n",
    "class WebPage(Page, HTMLPageMixin):\n",
    "    pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 76,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'<html><body>web content</body></html>'"
      ]
     },
     "execution_count": 76,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "page = WebPage(0, 'web content')\n",
    "page.to_html()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 다중 상속 시 주의점"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 77,
   "metadata": {},
   "outputs": [],
   "source": [
    "class A:\n",
    "    def hello(self):\n",
    "        print('Hello')\n",
    "\n",
    "class B(A):\n",
    "    def hello(self):\n",
    "        print('Hola')\n",
    "        super().hello()  # 베이스 클래스의 메서드를 실행\n",
    "\n",
    "class C(A):\n",
    "    def hello(self):\n",
    "        print('안녕하세요')\n",
    "        super().hello()  # 베이스 클래스의 메서드를 실행\n",
    "\n",
    "class D(B, C):\n",
    "    def hello(self):\n",
    "        print('Xin Chao')\n",
    "        super().hello()  # 베이스 클래스의 메서드를 실행"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 78,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Xin Chao\n",
      "Hola\n",
      "안녕하세요\n",
      "Hello\n"
     ]
    }
   ],
   "source": [
    "d = D()\n",
    "d.hello()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### \\_\\_mro\\_\\_ 이용한 시용한 메서드 결정 순서 확인"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 79,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(__main__.D, __main__.B, __main__.C, __main__.A, object)"
      ]
     },
     "execution_count": 79,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "D.__mro__  # 메서드 결정 순서 확인"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 80,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Xin Chao\n",
      "Hola\n",
      "안녕하세요\n",
      "Hello\n"
     ]
    }
   ],
   "source": [
    "d.hello()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 정리"
   ]
  }
 ],
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  "kernelspec": {
   "display_name": "Python 3",
   "language": "python",
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    "name": "ipython",
    "version": 3
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   "file_extension": ".py",
   "mimetype": "text/x-python",
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