EffectivePython-Metaclass-Validate-Register-Subclass.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 用元类验证子类"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<class '__main__.Meta'> Test () {'__module__': '__main__', '__qualname__': 'Test', 'hello': 'world', '__init__': <function Test.__init__ at 0x13f29d268>}\n"
     ]
    }
   ],
   "source": [
    "class Meta(type):\n",
    "    def __new__(metaclass, name, bases, class_dict):\n",
    "        print(metaclass, name, bases, class_dict)\n",
    "        return type.__new__(metaclass, name, bases, class_dict)\n",
    "\n",
    "class Test(metaclass=Meta):\n",
    "    hello = 'world'\n",
    "    def __init__(self, a, b):\n",
    "        self.a = a\n",
    "        self.b = b\n",
    "        print('Initiating Test Instance...')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [],
   "source": [
    "class ValidatePolygon(type):\n",
    "    def __new__(meta, name, bases, class_dict):\n",
    "        print(meta, name, bases, class_dict)\n",
    "        # 有父类的时候才验证，免得自己也被验证了\n",
    "        if bases:\n",
    "            if class_dict['sides'] < 3:\n",
    "                raise ValueError('Polygons need at least 3 sides')\n",
    "        return type.__new__(meta, name, bases, class_dict)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<class '__main__.ValidatePolygon'> Polygon () {'__module__': '__main__', '__qualname__': 'Polygon', 'sides': None, 'interior_angles': <classmethod object at 0x1400c8630>}\n",
      "<class '__main__.ValidatePolygon'> Triangle (<class '__main__.Polygon'>,) {'__module__': '__main__', '__qualname__': 'Triangle', 'sides': 3}\n",
      "<class '__main__.ValidatePolygon'> TwoSidesPolygon (<class '__main__.Polygon'>,) {'__module__': '__main__', '__qualname__': 'TwoSidesPolygon', 'sides': 3}\n"
     ]
    }
   ],
   "source": [
    "class Polygon(metaclass=ValidatePolygon):\n",
    "    sides = None\n",
    "    \n",
    "    @classmethod\n",
    "    def interior_angles(cls):\n",
    "        return (cls.sides - 2) * 180\n",
    "\n",
    "class Triangle(Polygon):\n",
    "    sides = 3\n",
    "    pass\n",
    "\n",
    "class TwoSidesPolygon(Polygon):\n",
    "    sides = 3"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 用元类注册子类"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "import json\n",
    "\n",
    "class Serializable:\n",
    "    def __init__(self, *args, **kwargs):\n",
    "        self.args = args\n",
    "        self.kwargs = kwargs\n",
    "    def serialize(self):\n",
    "        return json.dumps({'args': self.args, 'kwargs': self.kwargs})"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Deseiralizable(Serializable):\n",
    "    @classmethod\n",
    "    def deserialize(cls, json_data):\n",
    "        params = json.loads(json_data)\n",
    "        return cls(*params['args'], **params['kwargs'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Point2D(Deseiralizable):\n",
    "    def __init__(self, x, y):\n",
    "        super().__init__(x, y)\n",
    "        self.x = x\n",
    "        self.y = y\n",
    "    def __repr__(self):\n",
    "        return 'Point2D(%d, %d)' % (self.x, self.y)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{\"args\": [1, 2], \"kwargs\": {}}\n"
     ]
    }
   ],
   "source": [
    "p = Point2D(1, 2)\n",
    "data = p.serialize()\n",
    "print(data)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Point2D(1, 2)\n"
     ]
    }
   ],
   "source": [
    "p2 = Point2D.deserialize(data)\n",
    "# 不灵活，反序列化的时候需要事先知道类\n",
    "print(p2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [],
   "source": [
    "class BetterSerializable:\n",
    "    def __init__(self, *args, **kwargs):\n",
    "        self.args = args\n",
    "        self.kwargs = kwargs\n",
    "    def serialize(self):\n",
    "        data = {'target_class': self.__class__.__name__, 'args': self.args, 'kwargs': self.kwargs}\n",
    "        return json.dumps(data)\n",
    "\n",
    "class BetterPoint2D(BetterSerializable):\n",
    "    def __init__(self, x, y):\n",
    "        super().__init__(x, y)\n",
    "        self.x = x\n",
    "        self.y = y\n",
    "    def __repr__(self):\n",
    "        return f'<BetterPoint2D {self.x}, {self.y}>'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{\"target_class\": \"BetterPoint2D\", \"args\": [2, 3], \"kwargs\": {}}\n"
     ]
    }
   ],
   "source": [
    "bp = BetterPoint2D(2, 3)\n",
    "print(bp.serialize())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "registry = {}\n",
    "def registry_calss(cls):\n",
    "    registry[cls.__name__] = cls\n",
    "    \n",
    "def deserialize(json_data):\n",
    "    params = json.loads(json_data)\n",
    "    target_class = params['target_class']\n",
    "    if not target_class:\n",
    "        raise ValueError('Invalid data, target_class required')\n",
    "    if not target_class in registry:\n",
    "        raise ValueError('target_class is not registered')\n",
    "    return registry[target_class](*params['args'], **params['kwargs'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [],
   "source": [
    "registry_calss(BetterPoint2D)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<BetterPoint2D 3, 4>\n"
     ]
    }
   ],
   "source": [
    "bp = BetterPoint2D(3, 4)\n",
    "data = bp.serialize()\n",
    "bp2 = deserialize(data)\n",
    "print(bp2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'BetterPoint2D': <class '__main__.BetterPoint2D'>, 'BetterPoint3D': <class '__main__.BetterPoint3D'>}\n",
      "{\"target_class\": \"BetterPoint3D\", \"args\": [1, 2, 3], \"kwargs\": {}}\n",
      "<BetterPoint3D 1, 2, 3>\n"
     ]
    }
   ],
   "source": [
    "# 如果忘记注册这个类就会报错，用元类来自动注册\n",
    "class Meta(type):\n",
    "    def __new__(meta, name, bases, class_dict):\n",
    "        cls = type.__new__(meta, name, bases, class_dict)\n",
    "        registry[name] = cls\n",
    "        return cls\n",
    "\n",
    "class BetterPoint3D(BetterSerializable, metaclass=Meta):\n",
    "    def __init__(self, x, y, z):\n",
    "        super().__init__(x, y, z)\n",
    "        self.x = x\n",
    "        self.y = y\n",
    "        self.z = z\n",
    "    def __repr__(self):\n",
    "        return f'<BetterPoint3D {self.x}, {self.y}, {self.z}>'\n",
    "    \n",
    "print(registry)\n",
    "\n",
    "bp3 = BetterPoint3D(1, 2, 3)\n",
    "data = bp3.serialize()\n",
    "print(data)\n",
    "bp3 = deserialize(data)\n",
    "print(bp3)"
   ]
  }
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