Dataclasses

Datentypen in Python

Jason Myers

Instructor

Warum Dataclasses nutzen

Unterstützung für Standardwerte
Eigene Objekt-Darstellungen
Einfache Umwandlung in Tupel oder Dictionary
Eigene Properties
Eingefrorene Instanzen

Unsere erste Dataclass ansehen

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

Einfache Umwandlung in Tupel oder Dictionary

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)

Eigene Properties

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

Eigene Properties verwenden

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

peanut.value_of_goods

Decimal('9.6')

Eingefrorene Instanzen

@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'

Lass uns üben!

Datentypen in Python