如何使用数据类生成字段值? [英] How to use dataclasses to generate a field value?

问题描述

我有以下课程:

class WordItem:
    def __init__(self, phrase: str, word_type: WORD_TYPE):
        self.id = f'{phrase}_{word_type.name.lower()}'
        self.phrase = phrase
        self.word_type = word_type
        @classmethod

    def from_payload(cls, payload: Dict[str, Any]) -> 'WordItem':
        return cls(**payload)

如何将此类重写为数据类?

具体地说，应该如何声明id字段?它具有一个生成的值，而不是创建实例的代码所提供的字段.

Specifically, how should the id field be declared? It has a generated value, and is not a field that the code creating instances would provide.

推荐答案

只需将您的每个属性移到类上带有类型注释的声明中，该类已用

Just move each of your attributes to a type-annotated declaration on the class, where the class has been decorated with the @dataclasses.dataclass decorator.

您可以在 __post_init__方法;确保使用 对象:

from dataclasses import dataclass, field    

@dataclass
class WordItem:
    id: str = field(init=False)
    phrase: str
    word_type: WORD_TYPE

    def __post_init__(self):
        self.id = f'{self.phrase}_{self.word_type.name.lower()}'

演示:

>>> from types import SimpleNamespace
>>> wt = SimpleNamespace(name='Python')
>>> WordItem('await', wt)
WordItem(id='await_python', phrase='await', word_type=namespace(name='Python'))

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