How to hook properties with Python3 dataclasses.

How-to-hook-properties-with-Python3-dataclasses.ipynb

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   "source": [
    "# How to hook properties with Python3 dataclasses.\n",
    "- [Reconciling Dataclasses And Properties In Python](https://florimond.dev/en/posts/2018/10/reconciling-dataclasses-and-properties-in-python/)"
   ]
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      "Python 3.8.3\n"
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   "source": [
    "!python --version"
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   "cell_type": "markdown",
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    "## Use mypy to check for type errors.\n",
    "[nb-mypy](https://pypi.org/project/nb-mypy/)"
   ]
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      "Version 1.0.4\n"
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   "source": [
    "%load_ext nb_mypy"
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   "source": [
    "%nb_mypy On"
   ]
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   "id": "b6bb7d67-397f-453b-adfe-17a4f0ce2911",
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   "outputs": [],
   "source": [
    "from dataclasses import dataclass\n",
    "from typing import Optional, Union"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a56a8131-6e4e-4fd8-b680-5f5009440883",
   "metadata": {},
   "source": [
    "## Want to hook properties."
   ]
  },
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     "text": [
      "__init__: None\n",
      "getter: Barack\n",
      "name: Barack\n",
      "setter: Donald\n",
      "getter: Donald\n",
      "name Donald\n",
      "setter: Joe\n",
      "getter: Joe\n",
      "name: Joe\n",
      "{'_name': 'Joe'}\n",
      "------------------------------\n",
      "__init__: George\n",
      "getter: George\n",
      "name: George\n",
      "{'_name': 'George'}\n"
     ]
    }
   ],
   "source": [
    "class Test1:\n",
    "    def __init__(self, name: Optional[str] = None):\n",
    "        print('__init__:', name)\n",
    "        if name is None:\n",
    "            name = 'Barack'\n",
    "        self._name: Optional[str] = name\n",
    "\n",
    "    @property\n",
    "    def name(self) -> Optional[str]:\n",
    "        print('getter:', self._name)\n",
    "        return self._name\n",
    "\n",
    "    @name.setter\n",
    "    def name(self, name: str):\n",
    "        print('setter:', name)\n",
    "        self._name = name\n",
    "\n",
    "\n",
    "t = Test1(name=None)\n",
    "print('name:', t.name)\n",
    "t.name = 'Donald'\n",
    "print('name', t.name)\n",
    "t.name = 'Joe'\n",
    "print('name:', t.name)\n",
    "print(vars(t))\n",
    "print('-'*30)\n",
    "t = Test1(name='George')\n",
    "print('name:', t.name)\n",
    "print(vars(t))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "bec14645-a582-4db9-b042-fb563fd586d1",
   "metadata": {},
   "source": [
    "## How to do the same with dataclasses."
   ]
  },
  {
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     "text": [
      "setter: None\n",
      "__post_init__\n",
      "getter: None\n",
      "setter: Barack\n",
      "getter: Barack\n",
      "name: Barack\n",
      "setter: Donald\n",
      "getter: Donald\n",
      "name: Donald\n",
      "setter: Joe\n",
      "getter: Joe\n",
      "name: Joe\n",
      "{'_name': 'Joe'}\n",
      "------------------------------\n",
      "setter: George\n",
      "__post_init__\n",
      "getter: George\n",
      "getter: George\n",
      "name: George\n",
      "{'_name': 'George'}\n"
     ]
    }
   ],
   "source": [
    "@dataclass\n",
    "class Test2:\n",
    "    name: Optional[Union[str, property]] = None\n",
    "\n",
    "    def __post_init__(self):\n",
    "        print('__post_init__')\n",
    "        if self.name is None:\n",
    "            self.name = 'Barack'\n",
    "\n",
    "    def _get_name(self) -> Optional[str]:\n",
    "        print('getter:', self._name)\n",
    "        return self._name\n",
    "\n",
    "    def _set_name(self, name: str):\n",
    "        print('setter:', name)\n",
    "        self._name = name\n",
    "\n",
    "# Note that this must be a module-level call.\n",
    "Test2.name = property(Test2._get_name, Test2._set_name)\n",
    "\n",
    "t = Test2(name=None)\n",
    "print('name:', t.name)\n",
    "t.name = 'Donald'\n",
    "print('name:', t.name)\n",
    "t.name = 'Joe'\n",
    "print('name:', t.name)\n",
    "print(vars(t))\n",
    "print('-'*30)\n",
    "t = Test2(name='George')\n",
    "print('name:', t.name)\n",
    "print(vars(t))"
   ]
  }
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