{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "outputs": [
    {
     "data": {
      "text/plain": "'21.4.0'"
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import typing as T\n",
    "import attrs\n",
    "\n",
    "attrs.__version__"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "markdown",
   "source": [
    "## PyCharm Support\n",
    "\n",
    "PyCharm 很早就支持基于 ``attr.s`` API 的自动补全, 但 ``attrs`` 是 2021 年之后的新 API, Pycharm 2022.3 中 ``attrs.define`` 还不被 PyCharm 所接受."
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%% md\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "__init__() missing 1 required positional argument: 'id'",
     "output_type": "error",
     "traceback": [
      "\u001B[0;31m---------------------------------------------------------------------------\u001B[0m",
      "\u001B[0;31mTypeError\u001B[0m                                 Traceback (most recent call last)",
      "Input \u001B[0;32mIn [2]\u001B[0m, in \u001B[0;36m<cell line: 20>\u001B[0;34m()\u001B[0m\n\u001B[1;32m     16\u001B[0m     account: \u001B[38;5;28mstr\u001B[39m \u001B[38;5;241m=\u001B[39m attr\u001B[38;5;241m.\u001B[39mfield()\n\u001B[1;32m     19\u001B[0m \u001B[38;5;66;03m# move cursor in bracket and hit CMD + P to see hint\u001B[39;00m\n\u001B[0;32m---> 20\u001B[0m \u001B[43mBase\u001B[49m\u001B[43m(\u001B[49m\u001B[43m)\u001B[49m\n\u001B[1;32m     21\u001B[0m User()\n\u001B[1;32m     22\u001B[0m PaidUser(\u001B[38;5;28mid\u001B[39m\u001B[38;5;241m=\u001B[39m\u001B[38;5;124m\"\u001B[39m\u001B[38;5;124minvalid\u001B[39m\u001B[38;5;124m\"\u001B[39m, name\u001B[38;5;241m=\u001B[39m\u001B[38;5;124m\"\u001B[39m\u001B[38;5;124malice\u001B[39m\u001B[38;5;124m\"\u001B[39m, account\u001B[38;5;241m=\u001B[39m\u001B[38;5;124m\"\u001B[39m\u001B[38;5;124m1234\u001B[39m\u001B[38;5;124m\"\u001B[39m)\n",
      "\u001B[0;31mTypeError\u001B[0m: __init__() missing 1 required positional argument: 'id'"
     ]
    }
   ],
   "source": [
    "import attr\n",
    "\n",
    "\n",
    "@attr.s\n",
    "class Base:\n",
    "    id: int = attr.field()\n",
    "\n",
    "\n",
    "@attr.s\n",
    "class User(Base):\n",
    "    name: str = attr.field()\n",
    "\n",
    "\n",
    "@attr.s\n",
    "class PaidUser(User):\n",
    "    account: str = attr.field()\n",
    "\n",
    "\n",
    "# move cursor in bracket and hit CMD + P to see hint\n",
    "Base()\n",
    "User()\n",
    "PaidUser(id=\"invalid\", name=\"alice\", account=\"1234\")"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "source": [
    "@attr.s\n",
    "class User:\n",
    "    _id: 1 = attr.ib()\n",
    "    name: str = attr.ib()\n",
    "\n",
    "\n",
    "user = User(id=1, name=\"Alice\")\n",
    "print(user)\n",
    "print(user._id)"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "outputs": [
    {
     "data": {
      "text/plain": "{'name': 'alice'}"
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "@attr.s\n",
    "class Base:\n",
    "    _important_attr: T.List[str] = None\n",
    "\n",
    "    def to_dict(self) -> dict:\n",
    "        return {\n",
    "            k: v\n",
    "            for k, v in attr.asdict(self).items()\n",
    "            if k in self._important_attr\n",
    "        }\n",
    "\n",
    "\n",
    "@attr.s\n",
    "class Person(Base):\n",
    "    id: int = attr.ib()\n",
    "    name: str = attr.ib()\n",
    "\n",
    "    _important_attr = [\"name\"]\n",
    "\n",
    "\n",
    "person = Person(id=1, name=\"alice\")\n",
    "person.to_dict()"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "markdown",
   "source": [
    "## Immutable 和 Mutable\n",
    "\n",
    "所谓 Immutable 就是对象一旦被创建, 就无法被修改. 而 Mutable 则是对象被创建后, 其属性值是可以被修改的. 这里要注意的是, 如果对象的属性是 Mutable 的对象, 比如有个属性是列表, 你可以对列表本身进行修改, 但是不能给这个属性赋一个新的值.\n",
    "\n",
    "Immutable 的好处:\n",
    "\n",
    "1. 可以从机制上避免很多因为修改带来的错误.\n",
    "2. 对象可以被缓存, 可以被哈希, 可以用来当 Dict Key, 可以用来去重."
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%% md\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4, 5]\n"
     ]
    }
   ],
   "source": [
    "def sort_arr(arr: list):\n",
    "    arr.sort()\n",
    "    return arr\n",
    "\n",
    "\n",
    "@attr.s(frozen=True)\n",
    "class MyImmutableData:\n",
    "    arr: T.List[int] = attr.ib(factory=list, converter=sort_arr)\n",
    "\n",
    "\n",
    "my_immutable_data = MyImmutableData(arr=[3, 1, 4, 2])\n",
    "my_immutable_data.arr.append(5)\n",
    "print(my_immutable_data.arr)"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "markdown",
   "source": [
    "## Converter\n",
    "\n",
    "很多时候我们的一些属性被传入的时候我们希望对其做一些预处理. 例如将字符串 cast type 成整数, 将列表进行排序等. 而一旦我们的对象是 Mutable 的, Converter 机制就不是很好用了. 因为逻辑上你每次对属性进行修改时就应该运行 converter, 但是你如果用 ``self.my_attribute = ...`` 的方式赋值, converter 方法并不会被调用. 所以这时我建议将 Converter 函数都做成这个类的 classmethod, 然后如果你非要调用 ``self.my_attribute = ...`` 的时候,"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%% md\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4]\n"
     ]
    }
   ],
   "source": [
    "def sort_arr(arr: list):\n",
    "    arr.sort()\n",
    "    return arr\n",
    "\n",
    "\n",
    "@attr.s\n",
    "class MyMutableData:\n",
    "    arr: T.List[int] = attr.ib(factory=list, converter=sort_arr)\n",
    "\n",
    "    @classmethod\n",
    "    def convert_arr(cls, arr: list) -> list:\n",
    "        return sort_arr(arr)\n",
    "\n",
    "\n",
    "my_mutable_data = MyMutableData(arr=[1, 2])\n",
    "my_mutable_data.arr = my_mutable_data.convert_arr([3, 1, 4, 2])\n",
    "print(my_mutable_data.arr)"
   ],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "outputs": [],
   "source": [],
   "metadata": {
    "collapsed": false,
    "pycharm": {
     "name": "#%%\n"
    }
   }
  }
 ],
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   "codemirror_mode": {
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