Python 数据类 - dataclass 的作用与不足

https://docs.python.org/zh-cn/3/library/dataclasses.html
https://peps.python.org/pep-0526/
https://peps.python.org/pep-0557/

dataclass 简单示例

from dataclasses import dataclass


@dataclass
class User:
    name: str
    age: int


if __name__ == '__main__':
    response_json = {'name': 'python', 'age': 32}
    user = User(**response_json)
    print(user.name, user.age)  # python 32

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不用使用 dataclass 也可以

class User:
    def __init__(self, name: str, age: int):
        self.name = name
        self.age = age


if __name__ == '__main__':
    response_json = {'name': 'python', 'age': 32}
    user = User(**response_json)
    print(user.name, user.age)

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User 显得稍显麻烦，不过这里很简单，倒也无所谓。

dataclass 优势

1. dataclass 比直接使用 class 书写更简洁, 看起来一目了然
2. dataclass 自动实现实用方法，比如 __repr__
3. Pycharm 的完全代码提示

dataclass 的不足

不支持嵌套

from dataclasses import dataclass


@dataclass
class Info:
    sex: str
    phone: str
    address: str = None


@dataclass
class User:
    name: str
    age: int
    info: Info = None


if __name__ == '__main__':
    response_json = {
        'name': 'python',
        'age': 32,
        'info': {
            'sex': '',
            'phone': '',
            'address': 'https://python.org/'
        },
    }
    user = User(**response_json)
    # 显然这里我们期望的不是 dict
    assert isinstance(user.info, dict)

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不支持扩展字段

from dataclasses import dataclass


@dataclass
class User:
    name: str
    age: int


if __name__ == '__main__':
    response_json = {
        'name': 'python',
        'age': 32,
        'address': 'https://python.org/'
    }
    # TypeError: __init__() got an unexpected keyword argument 'address'
    user = User(**response_json)

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使用 datclass 库弥补这些不足

https://github.com/foyoux/datclass

pip install datclass
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datclass 简单示例

from dataclasses import dataclass

from datclass import DatClass


@dataclass
class Info(DatClass):
    sex: str
    phone: str
    address: str = None


@dataclass
class User(DatClass):
    name: str
    age: int
    info: Info = None


if __name__ == '__main__':
    response_json = {
        'name': 'python',
        'age': 32,
        'info': {
            'sex': '',
            'phone': '',
            'address': 'https://python.org/',
            'field': 'extra'
        },
    }
    user = User(**response_json)
    assert isinstance(user.info, Info)
    assert isinstance(user.info, Info)

    print(user.info.address)  # https://python.org/

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datclass 附带一个命令行命令用以自动生成 DatClass → datclass