Ch6_Descriptor.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Chapter 6. 디스크립터"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 개요\n",
    "### 디스크립터 메커니즘\n",
    "+ 최소 두 개의 클래스가 필요\n",
    "+ 디스크립터 프로토콜 중 하나를 구현한 클래스 인트턴스를 클래스 속성으로 포함해야 함\n",
    "    + \\_\\_get\\_\\_\n",
    "    + \\_\\_set\\_\\_\n",
    "    + \\_\\_delete\\_\\_\n",
    "    + \\_\\_set_name\\_\\_"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 디스크립터는 __get__ 매직 메서드의 결과를 반환함 \"\"\"\n",
    "\n",
    "import logging\n",
    "\n",
    "logging.basicConfig(level=logging.INFO)\n",
    "logger = logging.getLogger(__name__)\n",
    "\n",
    "class DescriptorClass:\n",
    "    def __get__(self, instance, owner): # owner의 인스턴스와 클래스를 받음\n",
    "        if instance is None:\n",
    "            return self\n",
    "        logger.info(\n",
    "            \"Call: %s.__get__(%r, %r)\", \n",
    "            self.__class__.__name__,\n",
    "            instance,\n",
    "            owner,\n",
    "        )\n",
    "        return instance\n",
    "\n",
    "\n",
    "class ClientClass:\n",
    "    descriptor = DescriptorClass()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "INFO:__main__:Call: DescriptorClass.__get__(<__main__.ClientClass object at 0x7fdd740bb2d0>, <class '__main__.ClientClass'>)\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<__main__.ClientClass at 0x7fdd740bb2d0>"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client = ClientClass()\n",
    "client.descriptor"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "INFO:__main__:Call: DescriptorClass.__get__(<__main__.ClientClass object at 0x7fdd740bb2d0>, <class '__main__.ClientClass'>)\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.descriptor is client"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 디스크립터 프로토콜의 매서드 \n",
    "#### \\_\\_get\\_\\_(self, instance, owner)\n",
    "+ owner가 있는 경우는 클래스에서 직접 호출하는 경우 instance가 None이기 때문"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 디스크립터를 인스턴스로 호출할 때와 클래스 속성으로 호출할 때의 차이점 \"\"\"\n",
    "\n",
    "class DescriptorClass:\n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self, owner\n",
    "        logger.info(\"Call: %s.__get__(%r, %r)\",\n",
    "                    self.__class__.__name__, instance, owner)\n",
    "        return instance\n",
    "    \n",
    "class ClientClass:\n",
    "    descriptor = DescriptorClass()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "INFO:__main__:Call: DescriptorClass.__get__(<__main__.ClientClass object at 0x7fdd7404f1d0>, <class '__main__.ClientClass'>)\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<__main__.ClientClass at 0x7fdd7404f1d0>"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ClientClass().descriptor"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(<__main__.DescriptorClass at 0x7fdd7404f490>, __main__.ClientClass)"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ClientClass.descriptor # instance가 None이므로 self를 반환"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### \\_\\_set\\_\\_(self, instance, value)\n",
    "+ 디스크립터에 값을 할당할 때 호출되며, \\_\\_set\\_\\_( ) 메서드를 구현한 디스크립터에 대해서만 활성화\n",
    "+ \\_\\_set\\_\\_이 구현되지 않은 경우 client.descriptor = \"value\" 에서 descriptor자체를 덮어쓸 수 있으므로 주의 필요"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "from typing import Callable, Any # 형 힌트 지원\n",
    "                                 # Callable[[Arg1Type, Arg2Type], ReturnType] \n",
    "\n",
    "class Validation: # 검증함수와 에러 메세지만을 가지고 있고 value는 __set__ 호출 시 전달받음\n",
    "    \"\"\"A configurable validation callable.\"\"\"\n",
    "\n",
    "    def __init__(\n",
    "        self, validation_function: Callable[[Any], bool], error_msg: str \n",
    "    ) -> None:\n",
    "        self.validation_function = validation_function\n",
    "        self.error_msg = error_msg\n",
    "\n",
    "    def __call__(self, value): # client.descriptor = 42 에서 42\n",
    "        if not self.validation_function(value):\n",
    "            raise ValueError(f\"{value!r} {self.error_msg}\")\n",
    "\n",
    "\n",
    "class Field:\n",
    "    \"\"\"A class attribute with validation functions configured over it.\"\"\"\n",
    "\n",
    "    def __init__(self, *validations):\n",
    "        self._name = None\n",
    "        self.validations = validations\n",
    "\n",
    "    def __set_name__(self, owner, name):\n",
    "        self._name = name\n",
    "\n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self\n",
    "        return instance.__dict__[self._name]\n",
    "\n",
    "    def validate(self, value):\n",
    "        for validation in self.validations:\n",
    "            validation(value)\n",
    "\n",
    "    def __set__(self, instance, value): # client.descriptor = 42 처럼 대입 시 실행됨\n",
    "        self.validate(value) # 여기서 raise ValueError 안된다면 다음 줄에서 대입됨\n",
    "        instance.__dict__[self._name] = value\n",
    "\n",
    "\n",
    "class ClientClass:\n",
    "    descriptor = Field(\n",
    "        Validation(lambda x: isinstance(x, (int, float)), \"is not a number\"),\n",
    "        Validation(lambda x: x >= 0, \"is not >= 0\"),\n",
    "    )"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "42\n"
     ]
    },
    {
     "ename": "ValueError",
     "evalue": "-42 is not >= 0",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-8-ebab0e0e1ebe>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[1;32m      3\u001b[0m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mclient\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdescriptor\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;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 5\u001b[0;31m \u001b[0mclient\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdescriptor\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m-\u001b[0m\u001b[0;36m42\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36m__set__\u001b[0;34m(self, instance, value)\u001b[0m\n\u001b[1;32m     36\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     37\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__set__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0minstance\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0;31m# client.descriptor = 42 처럼 대입 시 실행됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 38\u001b[0;31m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidate\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# 여기서 raise ValueError 안된다면 다음 줄에서 대입됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     39\u001b[0m         \u001b[0minstance\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m__dict__\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_name\u001b[0m\u001b[0;34m]\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[1;32m     40\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36mvalidate\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     33\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mvalidate\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     34\u001b[0m         \u001b[0;32mfor\u001b[0m \u001b[0mvalidation\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidations\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 35\u001b[0;31m             \u001b[0mvalidation\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[0m\u001b[1;32m     36\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     37\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__set__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0minstance\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0;31m# client.descriptor = 42 처럼 대입 시 실행됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36m__call__\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     13\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__call__\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;31m# client.descriptor = 42 에서 42\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     14\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0;32mnot\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidation_function\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[0;32m---> 15\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mValueError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34mf\"{value!r} {self.error_msg}\"\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     16\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     17\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: -42 is not >= 0"
     ]
    }
   ],
   "source": [
    "client = ClientClass()\n",
    "client.descriptor = 42\n",
    "print(client.descriptor)\n",
    "\n",
    "client.descriptor = -42"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "'string' is not a number",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-9-100e2bf81b13>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mclient\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mdescriptor\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m\"string\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36m__set__\u001b[0;34m(self, instance, value)\u001b[0m\n\u001b[1;32m     36\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     37\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__set__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0minstance\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0;31m# client.descriptor = 42 처럼 대입 시 실행됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 38\u001b[0;31m         \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidate\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# 여기서 raise ValueError 안된다면 다음 줄에서 대입됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     39\u001b[0m         \u001b[0minstance\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m__dict__\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_name\u001b[0m\u001b[0;34m]\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[1;32m     40\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36mvalidate\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     33\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mvalidate\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     34\u001b[0m         \u001b[0;32mfor\u001b[0m \u001b[0mvalidation\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidations\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 35\u001b[0;31m             \u001b[0mvalidation\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[0m\u001b[1;32m     36\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     37\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__set__\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0minstance\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mvalue\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0;31m# client.descriptor = 42 처럼 대입 시 실행됨\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;32m<ipython-input-7-3191205b50b2>\u001b[0m in \u001b[0;36m__call__\u001b[0;34m(self, value)\u001b[0m\n\u001b[1;32m     13\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m__call__\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;31m# client.descriptor = 42 에서 42\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     14\u001b[0m         \u001b[0;32mif\u001b[0m \u001b[0;32mnot\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mvalidation_function\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[0;32m---> 15\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mValueError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34mf\"{value!r} {self.error_msg}\"\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     16\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     17\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mValueError\u001b[0m: 'string' is not a number"
     ]
    }
   ],
   "source": [
    "client.descriptor = \"string\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### \\_\\_delete\\_\\_(self, instance)\n",
    "+ name과 email을 None으로 직접 설정하지 못하도록 \\_\\_set\\_\\_  함수 구현\n",
    "+ \\_\\_ delete\\_\\_ 를 통해서만 email의 None설정 가능"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [],
   "source": [
    "class ProtectedAttribute:\n",
    "    def __init__(self, requires_role=None) -> None:\n",
    "        self.permission_required = requires_role\n",
    "        self._name = None\n",
    "\n",
    "    def __set_name__(self, owner, name):\n",
    "        self._name = name\n",
    "\n",
    "    def __set__(self, user, value):\n",
    "        if value is None:\n",
    "            raise ValueError(f\"{self._name} can't be set to None\")\n",
    "        user.__dict__[self._name] = value\n",
    "\n",
    "    def __delete__(self, user):\n",
    "        if self.permission_required in user.permissions:\n",
    "            user.__dict__[self._name] = None\n",
    "        else:\n",
    "            raise ValueError(\n",
    "                f\"User {user!s} doesn't have {self.permission_required} \"\n",
    "                \"permission\"\n",
    "            )\n",
    "\n",
    "\n",
    "class User:\n",
    "    \"\"\"Only users with \"admin\" privileges can remove their email address.\"\"\"\n",
    "\n",
    "    email = ProtectedAttribute(requires_role=\"admin\")\n",
    "\n",
    "    def __init__(\n",
    "        self, username: str, email: str, permission_list: list = None\n",
    "    ) -> None:\n",
    "        self.username = username\n",
    "        self.email = email\n",
    "        self.permissions = permission_list or []\n",
    "\n",
    "    def __str__(self):\n",
    "        return self.username"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [],
   "source": [
    "admin = User(\"root\", \"root@d.com\", [\"admin\"])\n",
    "user = User(\"user\", \"user@d.com\", [\"email\", \"helpdesk\"])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 12,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "del admin.email\n",
    "admin.email is None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "User user doesn't have admin permission",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-13-c33f7427572a>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;32mdel\u001b[0m \u001b[0muser\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0memail\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-10-c39d2f1adcb5>\u001b[0m in \u001b[0;36m__delete__\u001b[0;34m(self, user)\u001b[0m\n\u001b[1;32m     17\u001b[0m         \u001b[0;32melse\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     18\u001b[0m             raise ValueError(\n\u001b[0;32m---> 19\u001b[0;31m                 \u001b[0;34mf\"User {user!s} doesn't have {self.permission_required} \"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m     20\u001b[0m                 \u001b[0;34m\"permission\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     21\u001b[0m             )\n",
      "\u001b[0;31mValueError\u001b[0m: User user doesn't have admin permission"
     ]
    }
   ],
   "source": [
    "del user.email"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### \\_\\_set_name\\_\\_(self, ower, name)\n",
    "+ 디스크립터가 처리하려는 속성의 이름을 알려줌\n",
    "+ 클래스 데코레이터, 메타클래스를 사용해야하는 종전의 방법을 개선함(3.6 부터)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 디스크립터의 유형\n",
    "+ \\_\\_set\\_\\__, \\_\\_delete\\_\\__ 메서드를 구현했다면 데이터 디스크립터로 구분됨\n",
    "+ \\_\\_get\\_\\__만 구현했다면 비데이터 디스크립터로 구분됨"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 비데이터 디스크립터\n",
    "+ set을 구현하지 않았으므로 객체의 사전이 우선 순위를 갖고 그 다음에 디스크립터가 실행됨"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "class NonDataDesciptor:\n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self\n",
    "        return 42\n",
    "    \n",
    "\n",
    "class ClientClass:\n",
    "    descriptor = NonDataDesciptor()   "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "42"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client = ClientClass()\n",
    "client.descriptor"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{}"
      ]
     },
     "execution_count": 16,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "vars(client) # 내부 딕셔너리에 아무것도 등록되지 않음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'descriptor': 99}"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.descriptor = 99\n",
    "vars(client)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "99"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.descriptor "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "42"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "del client.descriptor\n",
    "client.descriptor # 비데이터 디스크립터의 경우 내부 딕셔너리보다 후순위로 검색되는 것을 알 수 있음"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 데이터 디스크립터\n",
    "+ set을 구현했으므로 객체 사전보다 높은 우선순위를 갖게 됨\n",
    "+ 디스크립터의 set에서 setattr()이나 할당 표현식을 직접 사용하면 무한루프가 발생하므로 주의가 필요함"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [],
   "source": [
    "class DataDesciptor:\n",
    "    \n",
    "    def __init__(self):\n",
    "        self._name = None\n",
    "        \n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self\n",
    "        return 42\n",
    "    \n",
    "    def __set__(self, instance, value):\n",
    "        instance.__dict__[self._name] = value\n",
    "\n",
    "    def __set_name__(self, ower, name):\n",
    "        self._name = name    \n",
    "\n",
    "        \n",
    "class ClientClass:\n",
    "    descriptor = DataDesciptor()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "42"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client = ClientClass()\n",
    "client.descriptor"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{}"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "vars(client) # 내부 딕셔너리에 아무것도 등록되지 않음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'descriptor': 99}"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.descriptor = 99\n",
    "vars(client)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "42"
      ]
     },
     "execution_count": 24,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.descriptor # 내부 딕셔너리 보다도 우선순위가 높음, delete가 구현되어 있지 않으므로 del을 사용할 수 없음"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "99"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "client.__dict__[\"descriptor\"]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 디스크립터 실전\n",
    "+ 디스크립터는 클라이언트 클래스와 완전히 독립적이여야 함\n",
    "+ 어떠한 비즈니스 로직도 포함되어 있지 않아야 함\n",
    "+ 라이브러리, 프레임워크 또는 내부 API를 정의해야 함"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 여행지를 누적하는 디스크립터 \"\"\"\n",
    "\n",
    "class HistoryTracedAttribute:\n",
    "    \"\"\"Trace the values of this attribute into another one given by the name at\n",
    "    ``trace_attribute_name``.\n",
    "    \"\"\"\n",
    "\n",
    "    def __init__(self, trace_attribute_name: str) -> None:\n",
    "        self.trace_attribute_name = trace_attribute_name  # cities_visited\n",
    "        self._name = None\n",
    "\n",
    "    def __set_name__(self, owner, name):\n",
    "        self._name = name\n",
    "\n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self\n",
    "        return instance.__dict__[self._name] # current_city\n",
    "\n",
    "    def __set__(self, instance, value):\n",
    "        self._track_change_in_value_for_instance(instance, value)\n",
    "        instance.__dict__[self._name] = value # current_city\n",
    "\n",
    "    def _track_change_in_value_for_instance(self, instance, value):\n",
    "        self._set_default(instance)\n",
    "        if self._needs_to_track_change(instance, value):\n",
    "            instance.__dict__[self.trace_attribute_name].append(value) # 키값의 리스트에 여행을 추가\n",
    "\n",
    "    def _needs_to_track_change(self, instance, value) -> bool:\n",
    "        \"\"\"Determine if the value change needs to be traced or not.\n",
    "        Rules for adding a value to the trace:\n",
    "            * If the value is not previously set (it's the first one).\n",
    "            * If the new value is != than the current one.\n",
    "        \"\"\"\n",
    "        try:\n",
    "            current_value = instance.__dict__[self._name]\n",
    "        except KeyError: # 키가 없으면 발생\n",
    "            return True\n",
    "        return value != current_value # 현재 키값도 새로운 키값이 다른 경우에만 리스트에 추가하도록 True를 리턴함\n",
    "\n",
    "    def _set_default(self, instance):\n",
    "        instance.__dict__.setdefault(self.trace_attribute_name, []) # 키가 없으면 기본값으로 리스트를 반환\n",
    "\n",
    "\n",
    "class Traveller:\n",
    "    \"\"\"A person visiting several cities.\n",
    "    We wish to track the path of the traveller, as he or she is visiting each new city.\n",
    "    \"\"\"\n",
    "\n",
    "    current_city = HistoryTracedAttribute(\"cities_visited\")\n",
    "\n",
    "    def __init__(self, name, current_city):\n",
    "        self.name = name\n",
    "        self.current_city = current_city"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['Barcelona', 'Paris', 'Brussels', 'Amsterdam']"
      ]
     },
     "execution_count": 27,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "alice = Traveller(\"Alice\", \"Barcelona\")\n",
    "alice.current_city = \"Paris\"\n",
    "alice.current_city = \"Brussels\"\n",
    "alice.current_city = \"Brussels\"\n",
    "alice.current_city = \"Amsterdam\"\n",
    "alice.cities_visited"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Amsterdam'"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "alice.current_city"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### 클래스 데코레이터 피하기"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [],
   "source": [
    "from datetime import datetime\n",
    "from functools import partial\n",
    "from typing import Any, Callable\n",
    "\n",
    "\n",
    "class BaseFieldTransformation:\n",
    "    \"\"\"Base class to define descriptors that convert values.\"\"\"\n",
    "\n",
    "    def __init__(self, transformation: Callable[[Any, str], str]) -> None:\n",
    "        self._name = None\n",
    "        self.transformation = transformation\n",
    "\n",
    "    def __get__(self, instance, owner):\n",
    "        if instance is None:\n",
    "            return self\n",
    "        raw_value = instance.__dict__[self._name]\n",
    "        return self.transformation(raw_value)\n",
    "\n",
    "    def __set_name__(self, owner, name):\n",
    "        self._name = name\n",
    "\n",
    "    def __set__(self, instance, value):\n",
    "        instance.__dict__[self._name] = value\n",
    "\n",
    "\n",
    "ShowOriginal = partial(BaseFieldTransformation, transformation=lambda x: x) # transformation이 자동 설정됨\n",
    "HideField = partial(BaseFieldTransformation, transformation=lambda x: \"**redacted**\")\n",
    "FormatTime = partial(\n",
    "    BaseFieldTransformation,\n",
    "    transformation=lambda ft: ft.strftime(\"%Y-%m-%d %H:%M\"),\n",
    ")\n",
    "\n",
    "\n",
    "class LoginEvent:\n",
    "    username = ShowOriginal()\n",
    "    password = HideField()\n",
    "    ip = ShowOriginal()\n",
    "    timestamp = FormatTime()\n",
    "\n",
    "    def __init__(self, username, password, ip, timestamp):\n",
    "        self.username = username\n",
    "        self.password = password\n",
    "        self.ip = ip\n",
    "        self.timestamp = timestamp\n",
    "\n",
    "    def serialize(self):\n",
    "        return {\n",
    "            \"username\": self.username,\n",
    "            \"password\": self.password,\n",
    "            \"ip\": self.ip,\n",
    "            \"timestamp\": self.timestamp,\n",
    "        }\n",
    "\n",
    "\n",
    "class BaseEvent:\n",
    "    \"\"\"Abstract the serialization and the __init__\"\"\"\n",
    "\n",
    "    def __init__(self, **kwargs):\n",
    "        self.__dict__.update(kwargs)\n",
    "\n",
    "    def serialize(self):\n",
    "        return {\n",
    "            attr: getattr(self, attr) for attr in self._fields_to_serialize()\n",
    "        }\n",
    "\n",
    "    def _fields_to_serialize(self):\n",
    "        for attr_name, value in vars(self.__class__).items():\n",
    "            if isinstance(value, BaseFieldTransformation): # '__module__, __doc__ 등은 제외하고 변환함\n",
    "                yield attr_name\n",
    "\n",
    "\n",
    "class NewLoginEvent(BaseEvent):\n",
    "    \"\"\"A class that takes advantage of the base to only define the fields.\"\"\"\n",
    "\n",
    "    username = ShowOriginal()\n",
    "    password = HideField()\n",
    "    ip = ShowOriginal()\n",
    "    timestamp = FormatTime()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {},
   "outputs": [],
   "source": [
    "le = NewLoginEvent(username = \"usr\",\n",
    "                   password = \"secret password\",\n",
    "                   ip = \"127.0.0.1\",\n",
    "                   timestamp = datetime(2016, 7, 20, 15, 45))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'username': 'usr',\n",
       " 'password': '**redacted**',\n",
       " 'ip': '127.0.0.1',\n",
       " 'timestamp': '2016-07-20 15:45'}"
      ]
     },
     "execution_count": 31,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "le.serialize()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 파이썬 내부의 디스크립터 활용"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 함수와 메서드 \"\"\"\n",
    "\n",
    "class Method:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "        \n",
    "    def __call__(self, instance, arg1, arg2):\n",
    "        print(f\"{self.name}: {instance} 호출, 인자는 {arg1}과 {arg2}\")\n",
    "        \n",
    "class MyClass:\n",
    "    method = Method(\"Internal call\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "External call: <__main__.MyClass object at 0x7fdd7402d450> 호출, 인자는 1st과 2nd\n"
     ]
    }
   ],
   "source": [
    "instance = MyClass()\n",
    "Method(\"External call\")(instance, \"1st\", \"2nd\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "__call__() missing 1 required positional argument: 'arg2'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-34-0a430af22d62>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0minstance\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mmethod\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"1st\"\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m\"2nd\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mTypeError\u001b[0m: __call__() missing 1 required positional argument: 'arg2'"
     ]
    }
   ],
   "source": [
    "instance.method(\"1st\", \"2nd\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"\"\" 함수와 메서드, get을 구현하여 클래스 메소드로도 사용할 수 있도록 개선 \"\"\"\n",
    "from types import MethodType\n",
    "\n",
    "class Method:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "        \n",
    "    def __call__(self, instance, arg1, arg2):\n",
    "        print(f\"{self.name}: {instance} 호출, 인자는 {arg1}과 {arg2}\")\n",
    "        \n",
    "    def __get__(self, myclass_inst, myclass_cls):\n",
    "        if myclass_inst == None:\n",
    "            return self\n",
    "        else:\n",
    "            return MethodType(self, myclass_inst)\n",
    "        \n",
    "class MyClass:\n",
    "    method = Method(\"Internal call\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "External call: <__main__.MyClass object at 0x7fdd6d7d0190> 호출, 인자는 1st과 2nd\n",
      "Internal call: <__main__.MyClass object at 0x7fdd6d7d0190> 호출, 인자는 1st과 2nd\n"
     ]
    }
   ],
   "source": [
    "instance = MyClass()\n",
    "Method(\"External call\")(instance, \"1st\", \"2nd\")\n",
    "instance.method(\"1st\", \"2nd\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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