abc

Abstract Base Classes

Abstract base classes are standardized way to define interfaces in Python. They are used to define a minimal set of methods that a class must implement in order to be considered a duck type of the abstract base class.

• abc Documentation

Abstract Base Class Usage

from abc import ABC, abstractmethod

class Animal(ABC):
    @abstractmethod
    def speak(self):
        pass

The Animal class inherits from ABC and not from the object class. @abstractmethod decorator marks the speak method as abstract. Any class that inherits from Animal must implement the speak method.

Inheriting from an Abstract Base Class

class Cat(Animal):
    def speak(self):
        print('Meow')

>>> issubclass(Cat, Animal)
True

>>> cat = Cat()
>>> cat.speak()
Meow

Implementing no speak method

class Dog(Animal):
    def __init__(self, name):
        self.name = name

>>> dog = Dog('Buddy')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>

TypeError: Can't instantiate abstract class Dog with abstract methods speak

Abstract Properties

from abc import ABC, abstractproperty

class Animal(ABC):
    @abstractproperty
    def name(self):
        pass

The Animal class has an abstract property name. Any class that inherits from Animal must implement the name property.

class Dog(Animal):
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

>>> dog = Dog('Buddy')
>>> dog.name
'Buddy'

>>> dog.name = 'Buddy Jr.'
>>> dog.name
'Buddy Jr.'

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