Python3.7以降から導入されたdataclasses
本記事では、dataclassesの導入ポイントや使い方を紹介します

dataclassesとは？

dataclassesと定義する意義

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dataclassesの使い方

dataclassesの定義

from dataclasses import dataclass, field

@dataclass
class SampleDataClass:
    '''
    この記述が省略可能
    def __init__(self, id, name):
        self.ID = id
        self.NAME = name
    '''

    _id: int = 0
    _name: str = ''

dataclassesの初期化

data_1 = SampleDataClass(ID = 1, NAME="data_1")
print(data_1)
# SampleDataClass(ID=1, NAME='data_1')

dataclassesの参照、変更

data_1.NAME = "changed_data_1"
print(data_1)
# SampleDataClass(ID=1, NAME='changed_data_1')

dataclassesを変更不可にする

from dataclasses import dataclass, field

# frozen = Trueを追記
@dataclass(frozen = True)
class SampleDataClass:
    ID: int = 0
    NAME: str = ''


if __name__ == '__main__':
    data_1 = SampleDataClass(ID = 1, NAME="data_1")
    print(data_1)
    # SampleDataClass(ID=1, NAME='data_1')

    data_1.NAME = "changed_data_1"
    # frozen = True のため変更ができない
    # dataclasses.FrozenInstanceError: cannot assign to field 'NAME'

dataclassesのlist, dictの定義、初期化

from dataclasses import dataclass, field

@dataclass(frozen = True)
class SampleDataClass:

    ID: int = 0
    NAME: str = ''
    DATA_LIST: list = field(default_factory=list)
    DATA_DICT: dict = field(default_factory=dict)

if __name__ == '__main__':
    data_1 = SampleDataClass(
        ID = 1,
        NAME="data_1",
        DATA_LIST=["A", "B", "C"],
        DATA_DICT={"key_A":"value_A"})
    print(data_1)
    # SampleDataClass(ID=1, NAME='data_1', DATA_LIST=['A', 'B', 'C'], DATA_DICT={'key_A': 'value_A'})

さいごに