metaclass-etude.ipynb

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    "_class_table = {}\n",
    "class EntityMeta(type):\n",
    "    def __new__(mcs, name, bases, namespace):\n",
    "        cls = super().__new__(mcs, name, bases, namespace)\n",
    "        if 'name' in namespace:\n",
    "            _class_table[namespace['name']] = cls\n",
    "        return cls\n",
    "    \n",
    "    def __getitem__(self, key):\n",
    "        return _class_table[key]\n",
    "\n",
    "class Entity(metaclass=EntityMeta):\n",
    "    def __setattr__(self, key, value):\n",
    "        if '_fields' not in self.__dict__:\n",
    "            self.__dict__['_fields'] = []\n",
    "        self._fields.append(key)\n",
    "        super().__setattr__(key, value)\n",
    "    \n",
    "    def __str__(self):\n",
    "        fields = {n: getattr(self, n) for n in self._fields}\n",
    "        return f'<{self.__class__.__name__}: {fields}>'\n",
    "\n",
    "class Person(Entity):\n",
    "    name = 'person'\n",
    "    \n",
    "    def __init__(self, name, age):\n",
    "        self.name = name\n",
    "        self.age = age\n",
    "    \n",
    "    def greet(self):\n",
    "        print(f'Hello, {self.name}')\n",
    "\n",
    "class Plant(Entity):\n",
    "    name = 'plant'\n",
    "\n",
    "    def __init__(self, name, binomen):\n",
    "        self.name = name\n",
    "        self.binomen = binomen"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "<Person: {'name': 'Yuriko Nanao', 'age': 15}>\n",
      "<Plant: {'name': '白樺', 'binomen': 'Betula platyphylla'}>\n"
     ]
    }
   ],
   "source": [
    "print(Entity['person']('Yuriko Nanao', 15))\n",
    "print(Entity['plant']('白樺', 'Betula platyphylla'))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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