Abstract Base Classes

you should use abstract classes to specify which methods must be implemented by the child classes. The abc module "make sure" that you implement all those methods before being able to instantiate the objects.

def animate(animal):
	print(animal.get_sound())
	for leg in animal.legs_number:
		print("Moving leg", leg)
	print("Moved!")

from abc import ABC, abstractmethod
 
class Animal(ABC):
	
	@abstractmethod
	def get_sound(self) -> str:
		pass
	
	@property #  you need to add the @propertydecorator both in the abstract class and in every sub-class.
	@abstractmethod
	def legs_number(self) -> int:
		pass
 
# >>>a = Animal()
# Traceback (most recent call last):
#   File "c:\abstract_class.py", line 9, in <module>
#     a = Animal()
# TypeError: Can't instantiate abstract class Animal with abstract method get_sound
 
class Cat(Animal):
	
	def get_sound(self) -> str:
		return "Meow"
	
	@property #  you need to add the @propertydecorator both in the abstract class and in every sub-class.
	def legs_number(self) -> int:
  		return 4
 
# >>> a = Cat()
# >>> a.get_sound()
# Meow
 

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• Reference:
  • Level up Your Python Code with Abstract Classes

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Backlinks

• The Dependency Inversion Principle (DevLog)
• The Interface Segregation Principle (DevLog)
• The Open Closed Principle (DevLog)
• Protocol Classes (DevLog)