資料類別（dataclasses）

Python 的資料型別

Jason Myers

Instructor

為什麼用 dataclasses

支援預設值
自訂物件顯示
輕鬆轉為 tuple 或字典
自訂屬性
鎖定（凍結）實例

第一個 dataclass 範例

from dataclasses import dataclass

@dataclass
class Cookie:
    name: str
    quantity: int = 0

chocolate_chip = Cookie("chocolate chip", 13)
print(chocolate_chip.name)
print(chocolate_chip.quantity)

chocolate chip
13

輕鬆轉為 tuple 或字典

from dataclasses import asdict, astuple

ginger_molasses = Cookie("ginger molasses", 8)
asdict(ginger_molasses)

{'name': 'ginger molasses', 'quantity': 8}

astuple(ginger_molasses)

('ginger molasses', 8)

自訂屬性

from decimal import Decimal


@dataclass
class Cookie:
    name: str
    cost: Decimal
    quantity: int

   @property
   def value_of_goods(self):
      return int(self.quantity) * self.cost

使用自訂屬性

peanut = Cookie("peanut butter", Decimal("1.2"), 8)

peanut.value_of_goods

Decimal('9.6')

鎖定（Frozen）實例

@dataclass(frozen=True)
class Cookie:
    name: str
    quantity: int = 0

c = Cookie("chocolate chip", 10)

c.quantity = 15

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'quantity'

一起來練習吧！

Python 的資料型別